updade from Atlas repo

03-dict-set/index.py

@@ -5,8 +5,8 @@
 # tag::INDEX[]
 """Build an index mapping word -> list of occurrences"""
 
-import sys
 import re
+import sys
 
 WORD_RE = re.compile(r'\w+')
 
@@ -19,7 +19,7 @@ with open(sys.argv[1], encoding='utf-8') as fp:
             location = (line_no, column_no)
             index.setdefault(word, []).append(location)  # <1>
 
-# print in alphabetical order
+# display in alphabetical order
 for word in sorted(index, key=str.upper):
     print(word, index[word])
 # end::INDEX[]

03-dict-set/index0.py

@@ -5,8 +5,8 @@
 # tag::INDEX0[]
 """Build an index mapping word -> list of occurrences"""
 
-import sys
 import re
+import sys
 
 WORD_RE = re.compile(r'\w+')
 
@@ -22,7 +22,7 @@ with open(sys.argv[1], encoding='utf-8') as fp:
             occurrences.append(location)       # <2>
             index[word] = occurrences          # <3>
 
-# print in alphabetical order
+# display in alphabetical order
 for word in sorted(index, key=str.upper):  # <4>
     print(word, index[word])
 # end::INDEX0[]

03-dict-set/index_default.py

@@ -5,9 +5,9 @@
 # tag::INDEX_DEFAULT[]
 """Build an index mapping word -> list of occurrences"""
 
-import sys
-import re
 import collections
+import re
+import sys
 
 WORD_RE = re.compile(r'\w+')
 
@@ -20,7 +20,7 @@ with open(sys.argv[1], encoding='utf-8') as fp:
             location = (line_no, column_no)
             index[word].append(location)  # <2>
 
-# print in alphabetical order
+# display in alphabetical order
 for word in sorted(index, key=str.upper):
     print(word, index[word])
 # end::INDEX_DEFAULT[]

04-text-byte/categories.py

@@ -1,6 +1,6 @@
 import sys
 import collections
-from unicodedata import name, category
+from unicodedata import category
 
 
 def category_stats():

04-text-byte/default_encodings.py

@@ -1,4 +1,5 @@
-import sys, locale
+import locale
+import sys
 
 expressions = """
         locale.getpreferredencoding()

05-record-like/dataclass/coordinates.py

@@ -13,7 +13,6 @@ from dataclasses import dataclass
 
 @dataclass(frozen=True)
 class Coordinate:
-	
     lat: float
     long: float
 

08-def-type-hints/colors.py

@@ -76,6 +76,5 @@ def demo():
     print(n, name2hex(n, o))
 
 
-
 if __name__ == '__main__':
     demo()

08-def-type-hints/columnize2.py

@@ -10,7 +10,6 @@ def columnize(sequence: Sequence[T], num_columns: int = 0) -> List[Tuple[T, ...]
     return [tuple(sequence[i::num_rows]) for i in range(num_rows)]
 
 
-
 def demo() -> None:
     nato = ('Alfa Bravo Charlie Delta Echo Foxtrot Golf Hotel India'
             ' Juliett Kilo Lima Mike November Oscar Papa Quebec Romeo'
@@ -22,7 +21,6 @@ def demo() -> None:
             print(f'{word:15}', end='')
         print()
 
-
     print()
     for length in range(2, 21, 6):
         values = list(range(1, length + 1))

08-def-type-hints/columnize_alias.py

@@ -10,7 +10,6 @@ def columnize(sequence: Sequence[str], num_columns: int) -> List[Row]:
     return [tuple(sequence[i::num_rows]) for i in range(num_rows)]
 
 
-
 def demo() -> None:
     nato = ('Alfa Bravo Charlie Delta Echo Foxtrot Golf Hotel India'
             ' Juliett Kilo Lima Mike November Oscar Papa Quebec Romeo'

08-def-type-hints/comparable/mymax_test.py

@@ -1,4 +1,4 @@
-from typing import List, Callable, TypeVar
+from typing import List, Callable
 
 import pytest  # type: ignore
 

08-def-type-hints/double/double_test.py

@@ -53,4 +53,4 @@ def test_double_nparray() -> None:
 def test_double_none() -> None:
     given = None
     with pytest.raises(TypeError):
-        result = double(given)
+        double(given)

08-def-type-hints/mode/mode_T.py

@@ -12,7 +12,7 @@ def mode(data: Iterable[T]) -> T:
 
 
 def demo() -> None:
-    from typing import List, Set, TYPE_CHECKING
+    from typing import TYPE_CHECKING
     pop: list[set] = [set(), set()]
     m = mode(pop)
     if TYPE_CHECKING:
@@ -21,5 +21,6 @@ def demo() -> None:
     print(pop)
     print(repr(m), type(m))
 
+
 if __name__ == '__main__':
     demo()

08-def-type-hints/passdrill.py

@@ -3,12 +3,11 @@
 """passdrill: typing drills for practicing passphrases
 """
 
-import sys
 import os
+import sys
+from base64 import b64encode, b64decode
 from getpass import getpass
 from hashlib import scrypt
-from base64 import b64encode, b64decode
-
 from typing import Sequence, Tuple
 
 HASH_FILENAME = 'passdrill.hash'
@@ -20,7 +19,7 @@ def prompt() -> str:
     confirmed = ''
     while confirmed != 'y':
         passphrase = input('Type passphrase to hash (it will be echoed): ')
-        if passphrase == '' or passphrase == 'q':
+        if passphrase in ('', 'q'):
             print('ERROR: the passphrase cannot be empty or "q".')
             continue
         print(f'Passphrase to be hashed -> {passphrase}')
@@ -45,7 +44,7 @@ def save_hash() -> None:
     salted_hash = build_hash(prompt())
     with open(HASH_FILENAME, 'wb') as fp:
         fp.write(salted_hash)
-    print(f'Passphrase hash saved to', HASH_FILENAME)
+    print(f'Passphrase hash saved to {HASH_FILENAME}')
 
 
 def load_hash() -> Tuple[bytes, bytes]:

08-def-type-hints/typeddict/books.py

@@ -1,32 +0,0 @@
-# tag::BOOKDICT[]
-from typing import TypedDict, List
-import json
-
-class BookDict(TypedDict):
-    isbn: str
-    title: str
-    authors: List[str]
-    pagecount: int
-# end::BOOKDICT[]
-
-# tag::TOXML[]
-AUTHOR_EL = '<AUTHOR>{}</AUTHOR>'
-
-def to_xml(book: BookDict) -> str:  # <1>
-    elements: List[str] = []  # <2>
-    for key, value in book.items():
-        if isinstance(value, list):  # <3>
-            elements.extend(
-                AUTHOR_EL.format(n) for n in value)  # <4>
-        else:
-            tag = key.upper()
-            elements.append(f'<{tag}>{value}</{tag}>')
-    xml = '\n\t'.join(elements)
-    return f'<BOOK>\n\t{xml}\n</BOOK>'
-# end::TOXML[]
-
-# tag::FROMJSON[]
-def from_json(data: str) -> BookDict:
-    whatever: BookDict = json.loads(data)  # <1>
-    return whatever  # <2>
-# end::FROMJSON[]

08-def-type-hints/typeddict/books_any.py

@@ -1,32 +0,0 @@
-# tag::BOOKDICT[]
-from typing import TypedDict, List
-import json
-
-class BookDict(TypedDict):
-    isbn: str
-    title: str
-    authors: List[str]
-    pagecount: int
-# end::BOOKDICT[]
-
-# tag::TOXML[]
-AUTHOR_EL = '<AUTHOR>{}</AUTHOR>'
-
-def to_xml(book: BookDict) -> str:  # <1>
-    elements: List[str] = []  # <2>
-    for key, value in book.items():
-        if isinstance(value, list):  # <3>
-            elements.extend(AUTHOR_EL.format(n)
-                for n in value)
-        else:
-            tag = key.upper()
-            elements.append(f'<{tag}>{value}</{tag}>')
-    xml = '\n\t'.join(elements)
-    return f'<BOOK>\n\t{xml}\n</BOOK>'
-# end::TOXML[]
-
-# tag::FROMJSON[]
-def from_json(data: str) -> BookDict:
-    whatever = json.loads(data)  # <1>
-    return whatever  # <2>
-# end::FROMJSON[]

08-def-type-hints/typeddict/demo_books.py

@@ -1,20 +0,0 @@
-from books import BookDict
-from typing import TYPE_CHECKING
-
-def demo() -> None:  # <1>
-    book = BookDict(  # <2>
-        isbn='0134757599',
-        title='Refactoring, 2e',
-        authors=['Martin Fowler', 'Kent Beck'],
-        pagecount=478
-    )
-    authors = book['authors'] # <3>
-    if TYPE_CHECKING:  # <4>
-        reveal_type(authors)  # <5>
-    authors = 'Bob'  # <6>
-    book['weight'] = 4.2
-    del book['title']
-
-
-if __name__ == '__main__':
-    demo()

08-def-type-hints/typeddict/demo_not_book.py

@@ -1,23 +0,0 @@
-from books import to_xml, from_json
-from typing import TYPE_CHECKING
-
-def demo() -> None:
-    NOT_BOOK_JSON = """
-        {"title": "Andromeda Strain",
-         "flavor": "pistachio",
-         "authors": true}
-    """
-    not_book = from_json(NOT_BOOK_JSON)  # <1>
-    if TYPE_CHECKING:  # <2>
-        reveal_type(not_book)
-        reveal_type(not_book['authors'])
-
-    print(not_book)  # <3>
-    print(not_book['flavor'])  # <4>
-
-    xml = to_xml(not_book)  # <5>
-    print(xml)  # <6>
-
-
-if __name__ == '__main__':
-    demo()

08-def-type-hints/typeddict/test_books.py

@@ -1,112 +0,0 @@
-import json
-from typing import cast
-
-from books import BookDict, to_xml, from_json
-
-XML_SAMPLE = """
-<BOOK>
-\t<ISBN>0134757599</ISBN>
-\t<TITLE>Refactoring, 2e</TITLE>
-\t<AUTHOR>Martin Fowler</AUTHOR>
-\t<AUTHOR>Kent Beck</AUTHOR>
-\t<PAGECOUNT>478</PAGECOUNT>
-</BOOK>
-""".strip()
-
-
-# using plain dicts
-
-def test_1() -> None:
-    xml = to_xml({
-        'isbn': '0134757599',
-        'title': 'Refactoring, 2e',
-        'authors': ['Martin Fowler', 'Kent Beck'],
-        'pagecount': 478,
-    })
-    assert xml == XML_SAMPLE
-
-def test_2() -> None:
-    xml = to_xml(dict(
-        isbn='0134757599',
-        title='Refactoring, 2e',
-        authors=['Martin Fowler', 'Kent Beck'],
-        pagecount=478))
-    assert xml == XML_SAMPLE
-
-def test_5() -> None:
-    book_data: BookDict = dict(
-        isbn='0134757599',
-        title='Refactoring, 2e',
-        authors=['Martin Fowler', 'Kent Beck'],
-        pagecount=478
-    )
-    xml = to_xml(book_data)
-    assert xml == XML_SAMPLE
-
-def test_6() -> None:
-    book_data = dict(
-        isbn='0134757599',
-        title='Refactoring, 2e',
-        authors=['Martin Fowler', 'Kent Beck'],
-        pagecount=478
-    )
-    xml = to_xml(cast(BookDict, book_data))  # cast needed
-    assert xml == XML_SAMPLE
-
-def test_4() -> None:
-    xml = to_xml(BookDict(
-        isbn='0134757599',
-        title='Refactoring, 2e',
-        authors=['Martin Fowler', 'Kent Beck'],
-        pagecount=478))
-    assert xml == XML_SAMPLE
-
-def test_7() -> None:
-    book_data = BookDict(
-        isbn='0134757599',
-        title='Refactoring, 2e',
-        authors=['Martin Fowler', 'Kent Beck'],
-        pagecount=478
-    )
-    xml = to_xml(book_data)
-    assert xml == XML_SAMPLE
-
-def test_8() -> None:
-    book_data: BookDict = {
-        'isbn': '0134757599',
-        'title': 'Refactoring, 2e',
-        'authors': ['Martin Fowler', 'Kent Beck'],
-        'pagecount': 478,
-    }
-    xml = to_xml(book_data)
-    assert xml == XML_SAMPLE
-
-BOOK_JSON = """
-    {"isbn": "0134757599",
-     "title": "Refactoring, 2e",
-     "authors": ["Martin Fowler", "Kent Beck"],
-     "pagecount": 478}
-"""
-
-def test_load_book_0() -> None:
-    book_data: BookDict = json.loads(BOOK_JSON)  # typed var
-    xml = to_xml(book_data)
-    assert xml == XML_SAMPLE
-
-def test_load_book() -> None:
-    book_data = from_json(BOOK_JSON)
-    xml = to_xml(book_data)
-    assert xml == XML_SAMPLE
-
-
-NOT_BOOK_JSON = """
-    {"isbn": 3.141592653589793
-     "title": [1, 2, 3],
-     "authors": ["Martin Fowler", "Kent Beck"],
-     "flavor": "strawberry"}
-"""
-
-def test_load_not_book() -> None:
-    book_data: BookDict = json.loads(BOOK_JSON)  # typed var
-    xml = to_xml(book_data)
-    assert xml == XML_SAMPLE

08-def-type-hints/typeddict/test_books_check_fails.py

@@ -1,20 +0,0 @@
-from books import BookDict, to_xml
-
-XML_SAMPLE = """
-<BOOK>
-\t<ISBN>0134757599</ISBN>
-\t<TITLE>Refactoring, 2e</TITLE>
-\t<AUTHOR>Martin Fowler</AUTHOR>
-\t<AUTHOR>Kent Beck</AUTHOR>
-\t<PAGECOUNT>478</PAGECOUNT>
-</BOOK>
-""".strip()
-
-def test_3() -> None:
-    xml = to_xml(BookDict(dict([  # Expected keyword arguments, {...}, or dict(...) in TypedDict constructor
-        ('isbn', '0134757599'),
-        ('title', 'Refactoring, 2e'),
-        ('authors', ['Martin Fowler', 'Kent Beck']),
-        ('pagecount', 478),
-    ])))
-    assert xml == XML_SAMPLE

09-closure-deco/clockdeco_cls.py

@@ -41,4 +41,3 @@ if __name__ == '__main__':
     for i in range(3):
         snooze(.123)
 
-

10-dp-1class-func/monkeytype/classic_strategy_test.py

@@ -56,8 +56,7 @@ def test_large_order_promo_no_discount(customer_fidelity_0, cart_plain) -> None:
 
 
 def test_large_order_promo_with_discount(customer_fidelity_0) -> None:
-    cart = [LineItem(str(item_code), 1, 1.0)
+    cart = [LineItem(str(item_code), 1, 1.0) for item_code in range(10)]
-                     for item_code in range(10)]
     order = Order(customer_fidelity_0, cart, LargeOrderPromo())
     assert order.total() == 10.0
     assert order.due() == 9.3

10-dp-1class-func/untyped/strategy_best3.py

@@ -89,4 +89,3 @@ def best_promo(order):
 
 # end::STRATEGY_BEST3[]
 
-

12-seq-hacking/vector_v1.py

@@ -100,7 +100,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)  # <3>
         components = components[components.find('['):-1]  # <4>
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -113,7 +113,7 @@ class Vector:
         return tuple(self) == tuple(other)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))  # <6>
+        return math.hypot(*self)  # <6>
 
     def __bool__(self):
         return bool(abs(self))

12-seq-hacking/vector_v2.py

@@ -127,7 +127,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -140,7 +140,7 @@ class Vector:
         return tuple(self) == tuple(other)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __bool__(self):
         return bool(abs(self))

12-seq-hacking/vector_v3.py

@@ -170,7 +170,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -183,7 +183,7 @@ class Vector:
         return tuple(self) == tuple(other)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __bool__(self):
         return bool(abs(self))
@@ -207,8 +207,8 @@ class Vector:
             pos = cls.shortcut_names.find(name)  # <3>
             if 0 <= pos < len(self._components):  # <4>
                 return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'  # <5>
+        msg = f'{cls.__name__!r} object has no attribute {name!r}'  # <5>
-        raise AttributeError(msg.format(cls, name))
+        raise AttributeError(msg)
 # end::VECTOR_V3_GETATTR[]
 
 # tag::VECTOR_V3_SETATTR[]
@@ -216,7 +216,7 @@ class Vector:
         cls = type(self)
         if len(name) == 1:  # <1>
             if name in cls.shortcut_names:  # <2>
-                error = 'readonly attribute {attr_name!r}'
+                error = 'read-only attribute {attr_name!r}'
             elif name.islower():  # <3>
                 error = "can't set attributes 'a' to 'z' in {cls_name!r}"
             else:

12-seq-hacking/vector_v4.py

@@ -166,7 +166,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -184,7 +184,7 @@ class Vector:
         return functools.reduce(operator.xor, hashes, 0)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __bool__(self):
         return bool(abs(self))
@@ -207,8 +207,8 @@ class Vector:
             pos = cls.shortcut_names.find(name)
             if 0 <= pos < len(self._components):
                 return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'
+        msg = f'{cls.__name__!r} object has no attribute {name!r}'
-        raise AttributeError(msg.format(cls, name))
+        raise AttributeError(msg)
 
     @classmethod
     def frombytes(cls, octets):

12-seq-hacking/vector_v5.py

@@ -209,7 +209,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -227,7 +227,7 @@ class Vector:
         return functools.reduce(operator.xor, hashes, 0)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __bool__(self):
         return bool(abs(self))
@@ -250,11 +250,11 @@ class Vector:
             pos = cls.shortcut_names.find(name)
             if 0 <= pos < len(self._components):
                 return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'
+        msg = f'{cls.__name__!r} object has no attribute {name!r}'
-        raise AttributeError(msg.format(cls, name))
+        raise AttributeError(msg)
 
     def angle(self, n):  # <2>
-        r = math.sqrt(sum(x * x for x in self[n:]))
+        r = math.hypot(*self[n:])
         a = math.atan2(r, self[n-1])
         if (n == len(self) - 1) and (self[-1] < 0):
             return math.pi * 2 - a

13-protocol-abc/double/double_test.py

@@ -53,4 +53,4 @@ def test_double_nparray() -> None:
 def test_double_none() -> None:
     given = None
     with pytest.raises(TypeError):
-        result = double(given)
+        double(given)

13-protocol-abc/tombola.py

@@ -19,7 +19,6 @@ class Tombola(abc.ABC):  # <1>
         """Return `True` if there's at least 1 item, `False` otherwise."""
         return bool(self.inspect())  # <5>
 
-
     def inspect(self):
         """Return a sorted tuple with the items currently inside."""
         items = []

13-protocol-abc/typing/randompick_test.py

@@ -3,7 +3,7 @@ from typing import Any, Iterable, TYPE_CHECKING
 
 from randompick import RandomPicker  # <1>
 
-class SimplePicker():  # <2>
+class SimplePicker:  # <2>
     def __init__(self, items: Iterable) -> None:
         self._items = list(items)
         random.shuffle(self._items)

13-protocol-abc/typing/randompickload.py

@@ -1,4 +1,4 @@
-from typing import Protocol, runtime_checkable, Any, Iterable
+from typing import Protocol, runtime_checkable
 from randompick import RandomPicker
 
 @runtime_checkable  # <1>

13-protocol-abc/typing/randompickload_test.py

@@ -1,9 +1,9 @@
 import random
-from typing import Any, Iterable, TYPE_CHECKING
+from typing import Any, Iterable
 
 from randompickload import LoadableRandomPicker
 
-class SimplePicker():
+class SimplePicker:
     def __init__(self, items: Iterable) -> None:
         self._items = list(items)
         random.shuffle(self._items)
@@ -11,7 +11,7 @@ class SimplePicker():
     def pick(self) -> Any:
         return self._items.pop()
 
-class LoadablePicker():  # <1>
+class LoadablePicker:  # <1>
     def __init__(self, items: Iterable) -> None:
         self.load(items)
 

15-more-types/cafeteria.py

@@ -2,25 +2,25 @@ from typing import TypeVar, Generic
 
 
 class Beverage:
-    """Any beverage"""
+    """Any beverage."""
 
 
 class Juice(Beverage):
-    """Any fruit juice"""
+    """Any fruit juice."""
 
 
 class OrangeJuice(Juice):
-    """Delicious juice from Brazilian oranges"""
+    """Delicious juice from Brazilian oranges."""
 
 
-BeverageT = TypeVar('BeverageT', covariant=True)
+T_co = TypeVar('T_co', covariant=True)
 
 
-class BeverageDispenser(Generic[BeverageT]):
+class BeverageDispenser(Generic[T_co]):
-    def __init__(self, beverage: BeverageT) -> None:
+    def __init__(self, beverage: T_co) -> None:
         self.beverage = beverage
 
-    def dispense(self) -> BeverageT:
+    def dispense(self) -> T_co:
         return self.beverage
 
 
@@ -36,11 +36,11 @@ class Compostable(Biodegradable):
     """Compostable garbage."""
 
 
-GarbageT = TypeVar('GarbageT', contravariant=True)
+T_contra = TypeVar('T_contra', contravariant=True)
 
 
-class TrashCan(Generic[GarbageT]):
+class TrashCan(Generic[T_contra]):
-    def put(self, trash) -> None:
+    def put(self, trash: T_contra) -> None:
         """Store trash until dumped..."""
 
 
@@ -48,35 +48,48 @@ class Cafeteria:
     def __init__(
         self,
         dispenser: BeverageDispenser[Juice],
-        trash_can: TrashCan[Biodegradable]
+        trash_can: TrashCan[Biodegradable],
     ):
         """Initialize..."""
 
 
-beverage_dispenser = BeverageDispenser(Beverage())
+################################################ exact types
-juice_dispenser = BeverageDispenser(Juice())
-orange_juice_dispenser = BeverageDispenser(OrangeJuice())
 
-trash_can: TrashCan[Garbage] = TrashCan()
+juice_dispenser = BeverageDispenser(Juice())
 bio_can: TrashCan[Biodegradable] = TrashCan()
-compost_can: TrashCan[Compostable] = TrashCan()
 
 arnold_hall = Cafeteria(juice_dispenser, bio_can)
 
-######################## covariance on 1st argument
+
-arnold_hall = Cafeteria(orange_juice_dispenser, trash_can)
+################################################ covariant dispenser
+
+orange_juice_dispenser = BeverageDispenser(OrangeJuice())
+
+arnold_hall = Cafeteria(orange_juice_dispenser, bio_can)
+
+
+################################################ non-covariant dispenser
+
+beverage_dispenser = BeverageDispenser(Beverage())
 
 ## Argument 1 to "Cafeteria" has
 ## incompatible type "BeverageDispenser[Beverage]"
 ##          expected "BeverageDispenser[Juice]"
-# arnold_hall = Cafeteria(beverage_dispenser, trash_can)
+# arnold_hall = Cafeteria(beverage_dispenser, bio_can)
 
 
-######################## contravariance on 2nd argument
+################################################ contravariant trash
+
+trash_can: TrashCan[Garbage] = TrashCan()
+
+arnold_hall = Cafeteria(juice_dispenser, trash_can)
+
+
+################################################ non-contravariant trash
+
+compost_can: TrashCan[Compostable] = TrashCan()
 
 ## Argument 2 to "Cafeteria" has
 ## incompatible type "TrashCan[Compostable]"
 ##          expected "TrashCan[Biodegradable]"
 # arnold_hall = Cafeteria(juice_dispenser, compost_can)
-
-arnold_hall = Cafeteria(juice_dispenser, trash_can)

15-more-types/petbox/petbox.py

@@ -29,14 +29,6 @@ class Box(Generic[T]):
         return self.contents
 
 
-T_contra = TypeVar('T_contra', contravariant=True)
-
-
-class InBox(Generic[T_contra]):
-    def put(self, item: T) -> None:
-        self.contents = item
-
-
 T_co = TypeVar('T_co', covariant=True)
 
 
@@ -46,3 +38,11 @@ class OutBox(Generic[T_co]):
 
     def get(self) -> Any:
         return self.contents
+
+
+T_contra = TypeVar('T_contra', contravariant=True)
+
+
+class InBox(Generic[T_contra]):
+    def put(self, item: T) -> None:
+        self.contents = item

16-op-overloading/bingoaddable.py

@@ -53,34 +53,29 @@ Tests for __iadd__:
 """
 
 # tag::ADDABLE_BINGO[]
-import itertools  # <1>
-
 from tombola import Tombola
 from bingo import BingoCage
 
 
-class AddableBingoCage(BingoCage):  # <2>
+class AddableBingoCage(BingoCage):  # <1>
 
     def __add__(self, other):
-        if isinstance(other, Tombola):  # <3>
+        if isinstance(other, Tombola):  # <2>
             return AddableBingoCage(self.inspect() + other.inspect())
         else:
             return NotImplemented
 
     def __iadd__(self, other):
         if isinstance(other, Tombola):
-            other_iterable = other.inspect()  # <4>
+            other_iterable = other.inspect()  # <3>
         else:
             try:
-                other_iterable = iter(other)  # <5>
+                other_iterable = iter(other)  # <4>
-            except TypeError:  # <6>
+            except TypeError:  # <5>
                 self_cls = type(self).__name__
                 msg = "right operand in += must be {!r} or an iterable"
                 raise TypeError(msg.format(self_cls))
-        self.load(other_iterable)  # <7>
+        self.load(other_iterable)  # <6>
-        return self  # <8>
+        return self  # <7>
-
-
-
 
 # end::ADDABLE_BINGO[]

16-op-overloading/tombola.py

@@ -19,7 +19,6 @@ class Tombola(abc.ABC):  # <1>
         """Return `True` if there's at least 1 item, `False` otherwise."""
         return bool(self.inspect())  # <5>
 
-
     def inspect(self):
         """Return a sorted tuple with the items currently inside."""
         items = []
@@ -31,5 +30,5 @@ class Tombola(abc.ABC):  # <1>
         self.load(items)  # <7>
         return tuple(sorted(items))
 
-
 # END TOMBOLA_ABC
+

16-op-overloading/vector_py3_5.py

@@ -1,431 +0,0 @@
-"""
-A multi-dimensional ``Vector`` class, take 9: operator ``@``
-
-WARNING: This example requires Python 3.5 or later.
-
-A ``Vector`` is built from an iterable of numbers::
-
-    >>> Vector([3.1, 4.2])
-    Vector([3.1, 4.2])
-    >>> Vector((3, 4, 5))
-    Vector([3.0, 4.0, 5.0])
-    >>> Vector(range(10))
-    Vector([0.0, 1.0, 2.0, 3.0, 4.0, ...])
-
-
-Tests with 2-dimensions (same results as ``vector2d_v1.py``)::
-
-    >>> v1 = Vector([3, 4])
-    >>> x, y = v1
-    >>> x, y
-    (3.0, 4.0)
-    >>> v1
-    Vector([3.0, 4.0])
-    >>> v1_clone = eval(repr(v1))
-    >>> v1 == v1_clone
-    True
-    >>> print(v1)
-    (3.0, 4.0)
-    >>> octets = bytes(v1)
-    >>> octets
-    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
-    >>> abs(v1)
-    5.0
-    >>> bool(v1), bool(Vector([0, 0]))
-    (True, False)
-
-
-Test of ``.frombytes()`` class method:
-
-    >>> v1_clone = Vector.frombytes(bytes(v1))
-    >>> v1_clone
-    Vector([3.0, 4.0])
-    >>> v1 == v1_clone
-    True
-
-
-Tests with 3-dimensions::
-
-    >>> v1 = Vector([3, 4, 5])
-    >>> x, y, z = v1
-    >>> x, y, z
-    (3.0, 4.0, 5.0)
-    >>> v1
-    Vector([3.0, 4.0, 5.0])
-    >>> v1_clone = eval(repr(v1))
-    >>> v1 == v1_clone
-    True
-    >>> print(v1)
-    (3.0, 4.0, 5.0)
-    >>> abs(v1)  # doctest:+ELLIPSIS
-    7.071067811...
-    >>> bool(v1), bool(Vector([0, 0, 0]))
-    (True, False)
-
-
-Tests with many dimensions::
-
-    >>> v7 = Vector(range(7))
-    >>> v7
-    Vector([0.0, 1.0, 2.0, 3.0, 4.0, ...])
-    >>> abs(v7)  # doctest:+ELLIPSIS
-    9.53939201...
-
-
-Test of ``.__bytes__`` and ``.frombytes()`` methods::
-
-    >>> v1 = Vector([3, 4, 5])
-    >>> v1_clone = Vector.frombytes(bytes(v1))
-    >>> v1_clone
-    Vector([3.0, 4.0, 5.0])
-    >>> v1 == v1_clone
-    True
-
-
-Tests of sequence behavior::
-
-    >>> v1 = Vector([3, 4, 5])
-    >>> len(v1)
-    3
-    >>> v1[0], v1[len(v1)-1], v1[-1]
-    (3.0, 5.0, 5.0)
-
-
-Test of slicing::
-
-    >>> v7 = Vector(range(7))
-    >>> v7[-1]
-    6.0
-    >>> v7[1:4]
-    Vector([1.0, 2.0, 3.0])
-    >>> v7[-1:]
-    Vector([6.0])
-    >>> v7[1,2]
-    Traceback (most recent call last):
-      ...
-    TypeError: Vector indices must be integers
-
-
-Tests of dynamic attribute access::
-
-    >>> v7 = Vector(range(10))
-    >>> v7.x
-    0.0
-    >>> v7.y, v7.z, v7.t
-    (1.0, 2.0, 3.0)
-
-Dynamic attribute lookup failures::
-
-    >>> v7.k
-    Traceback (most recent call last):
-      ...
-    AttributeError: 'Vector' object has no attribute 'k'
-    >>> v3 = Vector(range(3))
-    >>> v3.t
-    Traceback (most recent call last):
-      ...
-    AttributeError: 'Vector' object has no attribute 't'
-    >>> v3.spam
-    Traceback (most recent call last):
-      ...
-    AttributeError: 'Vector' object has no attribute 'spam'
-
-
-Tests of hashing::
-
-    >>> v1 = Vector([3, 4])
-    >>> v2 = Vector([3.1, 4.2])
-    >>> v3 = Vector([3, 4, 5])
-    >>> v6 = Vector(range(6))
-    >>> hash(v1), hash(v3), hash(v6)
-    (7, 2, 1)
-
-
-Most hash codes of non-integers vary from a 32-bit to 64-bit Python build::
-
-    >>> import sys
-    >>> hash(v2) == (384307168202284039 if sys.maxsize > 2**32 else 357915986)
-    True
-
-
-Tests of ``format()`` with Cartesian coordinates in 2D::
-
-    >>> v1 = Vector([3, 4])
-    >>> format(v1)
-    '(3.0, 4.0)'
-    >>> format(v1, '.2f')
-    '(3.00, 4.00)'
-    >>> format(v1, '.3e')
-    '(3.000e+00, 4.000e+00)'
-
-
-Tests of ``format()`` with Cartesian coordinates in 3D and 7D::
-
-    >>> v3 = Vector([3, 4, 5])
-    >>> format(v3)
-    '(3.0, 4.0, 5.0)'
-    >>> format(Vector(range(7)))
-    '(0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0)'
-
-
-Tests of ``format()`` with spherical coordinates in 2D, 3D and 4D::
-
-    >>> format(Vector([1, 1]), 'h')  # doctest:+ELLIPSIS
-    '<1.414213..., 0.785398...>'
-    >>> format(Vector([1, 1]), '.3eh')
-    '<1.414e+00, 7.854e-01>'
-    >>> format(Vector([1, 1]), '0.5fh')
-    '<1.41421, 0.78540>'
-    >>> format(Vector([1, 1, 1]), 'h')  # doctest:+ELLIPSIS
-    '<1.73205..., 0.95531..., 0.78539...>'
-    >>> format(Vector([2, 2, 2]), '.3eh')
-    '<3.464e+00, 9.553e-01, 7.854e-01>'
-    >>> format(Vector([0, 0, 0]), '0.5fh')
-    '<0.00000, 0.00000, 0.00000>'
-    >>> format(Vector([-1, -1, -1, -1]), 'h')  # doctest:+ELLIPSIS
-    '<2.0, 2.09439..., 2.18627..., 3.92699...>'
-    >>> format(Vector([2, 2, 2, 2]), '.3eh')
-    '<4.000e+00, 1.047e+00, 9.553e-01, 7.854e-01>'
-    >>> format(Vector([0, 1, 0, 0]), '0.5fh')
-    '<1.00000, 1.57080, 0.00000, 0.00000>'
-
-
-Basic tests of operator ``+``::
-
-    >>> v1 = Vector([3, 4, 5])
-    >>> v2 = Vector([6, 7, 8])
-    >>> v1 + v2
-    Vector([9.0, 11.0, 13.0])
-    >>> v1 + v2 == Vector([3+6, 4+7, 5+8])
-    True
-    >>> v3 = Vector([1, 2])
-    >>> v1 + v3  # short vectors are filled with 0.0 on addition
-    Vector([4.0, 6.0, 5.0])
-
-
-Tests of ``+`` with mixed types::
-
-    >>> v1 + (10, 20, 30)
-    Vector([13.0, 24.0, 35.0])
-    >>> from vector2d_v3 import Vector2d
-    >>> v2d = Vector2d(1, 2)
-    >>> v1 + v2d
-    Vector([4.0, 6.0, 5.0])
-
-
-Tests of ``+`` with mixed types, swapped operands::
-
-    >>> (10, 20, 30) + v1
-    Vector([13.0, 24.0, 35.0])
-    >>> from vector2d_v3 import Vector2d
-    >>> v2d = Vector2d(1, 2)
-    >>> v2d + v1
-    Vector([4.0, 6.0, 5.0])
-
-
-Tests of ``+`` with an unsuitable operand:
-
-    >>> v1 + 1
-    Traceback (most recent call last):
-      ...
-    TypeError: unsupported operand type(s) for +: 'Vector' and 'int'
-    >>> v1 + 'ABC'
-    Traceback (most recent call last):
-      ...
-    TypeError: unsupported operand type(s) for +: 'Vector' and 'str'
-
-
-Basic tests of operator ``*``::
-
-    >>> v1 = Vector([1, 2, 3])
-    >>> v1 * 10
-    Vector([10.0, 20.0, 30.0])
-    >>> 10 * v1
-    Vector([10.0, 20.0, 30.0])
-
-
-Tests of ``*`` with unusual but valid operands::
-
-    >>> v1 * True
-    Vector([1.0, 2.0, 3.0])
-    >>> from fractions import Fraction
-    >>> v1 * Fraction(1, 3)  # doctest:+ELLIPSIS
-    Vector([0.3333..., 0.6666..., 1.0])
-
-
-Tests of ``*`` with unsuitable operands::
-
-    >>> v1 * (1, 2)
-    Traceback (most recent call last):
-      ...
-    TypeError: can't multiply sequence by non-int of type 'Vector'
-
-
-Tests of operator `==`::
-
-    >>> va = Vector(range(1, 4))
-    >>> vb = Vector([1.0, 2.0, 3.0])
-    >>> va == vb
-    True
-    >>> vc = Vector([1, 2])
-    >>> from vector2d_v3 import Vector2d
-    >>> v2d = Vector2d(1, 2)
-    >>> vc == v2d
-    True
-    >>> va == (1, 2, 3)
-    False
-
-
-Tests of operator `!=`::
-
-    >>> va != vb
-    False
-    >>> vc != v2d
-    False
-    >>> va != (1, 2, 3)
-    True
-
-
-Tests for operator `@` (Python >= 3.5), computing the dot product::
-
-    >>> va = Vector([1, 2, 3])
-    >>> vz = Vector([5, 6, 7])
-    >>> va @ vz == 38.0  # 1*5 + 2*6 + 3*7
-    True
-    >>> [10, 20, 30] @ vz
-    380.0
-    >>> va @ 3
-    Traceback (most recent call last):
-      ...
-    TypeError: unsupported operand type(s) for @: 'Vector' and 'int'
-
-
-"""
-
-from array import array
-import reprlib
-import math
-import functools
-import operator
-import itertools
-import numbers
-
-
-class Vector:
-    typecode = 'd'
-
-    def __init__(self, components):
-        self._components = array(self.typecode, components)
-
-    def __iter__(self):
-        return iter(self._components)
-
-    def __repr__(self):
-        components = reprlib.repr(self._components)
-        components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
-
-    def __str__(self):
-        return str(tuple(self))
-
-    def __bytes__(self):
-        return (bytes([ord(self.typecode)]) +
-                bytes(self._components))
-
-    def __eq__(self, other):
-        if isinstance(other, Vector):
-            return (len(self) == len(other) and
-                    all(a == b for a, b in zip(self, other)))
-        else:
-            return NotImplemented
-
-    def __hash__(self):
-        hashes = (hash(x) for x in self)
-        return functools.reduce(operator.xor, hashes, 0)
-
-    def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
-
-    def __bool__(self):
-        return bool(abs(self))
-
-    def __len__(self):
-        return len(self._components)
-
-    def __getitem__(self, index):
-        cls = type(self)
-        if isinstance(index, slice):
-            return cls(self._components[index])
-        elif isinstance(index, int):
-            return self._components[index]
-        else:
-            msg = '{.__name__} indices must be integers'
-            raise TypeError(msg.format(cls))
-
-    shortcut_names = 'xyzt'
-
-    def __getattr__(self, name):
-        cls = type(self)
-        if len(name) == 1:
-            pos = cls.shortcut_names.find(name)
-            if 0 <= pos < len(self._components):
-                return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'
-        raise AttributeError(msg.format(cls, name))
-
-    def angle(self, n):
-        r = math.sqrt(sum(x * x for x in self[n:]))
-        a = math.atan2(r, self[n-1])
-        if (n == len(self) - 1) and (self[-1] < 0):
-            return math.pi * 2 - a
-        else:
-            return a
-
-    def angles(self):
-        return (self.angle(n) for n in range(1, len(self)))
-
-    def __format__(self, fmt_spec=''):
-        if fmt_spec.endswith('h'):  # hyperspherical coordinates
-            fmt_spec = fmt_spec[:-1]
-            coords = itertools.chain([abs(self)],
-                                     self.angles())
-            outer_fmt = '<{}>'
-        else:
-            coords = self
-            outer_fmt = '({})'
-        components = (format(c, fmt_spec) for c in coords)
-        return outer_fmt.format(', '.join(components))
-
-    @classmethod
-    def frombytes(cls, octets):
-        typecode = chr(octets[0])
-        memv = memoryview(octets[1:]).cast(typecode)
-        return cls(memv)
-
-    def __add__(self, other):
-        try:
-            pairs = itertools.zip_longest(self, other, fillvalue=0.0)
-            return Vector(a + b for a, b in pairs)
-        except TypeError:
-            return NotImplemented
-
-    def __radd__(self, other):
-        return self + other
-
-    def __mul__(self, scalar):
-        if isinstance(scalar, numbers.Real):
-            return Vector(n * scalar for n in self)
-        else:
-            return NotImplemented
-
-    def __rmul__(self, scalar):
-        return self * scalar
-
-    def __matmul__(self, other):
-        try:
-            return sum(a * b for a, b in zip(self, other))
-        except TypeError:
-            return NotImplemented
-
-    def __rmatmul__(self, other):
-        return self @ other  # this only works in Python 3.5

16-op-overloading/vector_v6.py

@@ -264,7 +264,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -283,7 +283,7 @@ class Vector:
 
 # tag::VECTOR_V6_UNARY[]
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __neg__(self):
         return Vector(-x for x in self)  # <1>
@@ -313,11 +313,11 @@ class Vector:
             pos = cls.shortcut_names.find(name)
             if 0 <= pos < len(self._components):
                 return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'
+        msg = f'{cls.__name__!r} object has no attribute {name!r}'
-        raise AttributeError(msg.format(cls, name))
+        raise AttributeError(msg)
 
     def angle(self, n):
-        r = math.sqrt(sum(x * x for x in self[n:]))
+        r = math.hypot(*self[n:])
         a = math.atan2(r, self[n-1])
         if (n == len(self) - 1) and (self[-1] < 0):
             return math.pi * 2 - a

16-op-overloading/vector_v7.py

@@ -316,7 +316,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -334,7 +334,7 @@ class Vector:
         return functools.reduce(operator.xor, hashes, 0)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __neg__(self):
         return Vector(-x for x in self)
@@ -363,11 +363,11 @@ class Vector:
             pos = cls.shortcut_names.find(name)
             if 0 <= pos < len(self._components):
                 return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'
+        msg = f'{cls.__name__!r} object has no attribute {name!r}'
-        raise AttributeError(msg.format(cls, name))
+        raise AttributeError(msg)
 
     def angle(self, n):
-        r = math.sqrt(sum(x * x for x in self[n:]))
+        r = math.hypot(*self[n:])
         a = math.atan2(r, self[n-1])
         if (n == len(self) - 1) and (self[-1] < 0):
             return math.pi * 2 - a

16-op-overloading/vector_v8.py

@@ -317,7 +317,7 @@ class Vector:
     def __repr__(self):
         components = reprlib.repr(self._components)
         components = components[components.find('['):-1]
-        return 'Vector({})'.format(components)
+        return f'Vector({components})'
 
     def __str__(self):
         return str(tuple(self))
@@ -340,7 +340,7 @@ class Vector:
         return functools.reduce(operator.xor, hashes, 0)
 
     def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))
+        return math.hypot(*self)
 
     def __neg__(self):
         return Vector(-x for x in self)
@@ -369,11 +369,11 @@ class Vector:
             pos = cls.shortcut_names.find(name)
             if 0 <= pos < len(self._components):
                 return self._components[pos]
-        msg = '{.__name__!r} object has no attribute {!r}'
+        msg = f'{cls.__name__!r} object has no attribute {name!r}'
-        raise AttributeError(msg.format(cls, name))
+        raise AttributeError(msg)
 
     def angle(self, n):
-        r = math.sqrt(sum(x * x for x in self[n:]))
+        r = math.hypot(*self[n:])
         a = math.atan2(r, self[n-1])
         if (n == len(self) - 1) and (self[-1] < 0):
             return math.pi * 2 - a

17-it-generator/fibo_by_hand.py

@@ -44,8 +44,9 @@ def fibonacci():
 if __name__ == '__main__':
 
     for x, y in zip(Fibonacci(), fibonacci()):
-        assert x == y, '%s != %s' % (x, y)
+        assert x == y, f'{x} != {y}'
         print(x)
         if x > 10**10:
             break
     print('etc...')
+

17-it-generator/sentence_gen2.py

@@ -6,7 +6,7 @@ Sentence: iterate over words using a generator function
 import re
 import reprlib
 
-RE_WORD = re.compile('r\w+')
+RE_WORD = re.compile(r'\w+')
 
 
 class Sentence:
@@ -15,7 +15,7 @@ class Sentence:
         self.text = text  # <1>
 
     def __repr__(self):
-        return 'Sentence(%s)' % reprlib.repr(self.text)
+        return f'Sentence({reprlib.repr(self.text)})'
 
     def __iter__(self):
         for match in RE_WORD.finditer(self.text):  # <2>

17-it-generator/sentence_genexp.py

@@ -15,7 +15,7 @@ class Sentence:
         self.text = text
 
     def __repr__(self):
-        return 'Sentence(%s)' % reprlib.repr(self.text)
+        return f'Sentence({reprlib.repr(self.text)})'
 
     def __iter__(self):
         return (match.group() for match in RE_WORD.finditer(self.text))
@@ -29,7 +29,7 @@ def main():
         filename = sys.argv[1]
         word_number = int(sys.argv[2])
     except (IndexError, ValueError):
-        print('Usage: %s <file-name> <word-number>' % sys.argv[0])
+        print(f'Usage: {sys.argv[0]} <file-name> <word-number>')
         sys.exit(2)  # command line usage error
     with open(filename, 'rt', encoding='utf-8') as text_file:
         s = Sentence(text_file.read())
@@ -38,7 +38,7 @@ def main():
             print(word)
             break
     else:
-        warnings.warn('last word is #%d, "%s"' % (n, word))
+        warnings.warn(f'last word is #{n}, {word!r}')
 
 if __name__ == '__main__':
     main()

17-it-generator/sentence_iter.py

@@ -19,7 +19,7 @@ class Sentence:
         self.words = RE_WORD.findall(text)
 
     def __repr__(self):
-        return 'Sentence(%s)' % reprlib.repr(self.text)
+        return f'Sentence({reprlib.repr(self.text)})'
 
     def __iter__(self):  # <1>
         return SentenceIterator(self.words)  # <2>
@@ -50,7 +50,7 @@ def main():
         filename = sys.argv[1]
         word_number = int(sys.argv[2])
     except (IndexError, ValueError):
-        print('Usage: %s <file-name> <word-number>' % sys.argv[0])
+        print(f'Usage: {sys.argv[0]} <file-name> <word-number>')
         sys.exit(2)  # command line usage error
     with open(filename, 'rt', encoding='utf-8') as text_file:
         s = Sentence(text_file.read())
@@ -59,7 +59,7 @@ def main():
             print(word)
             break
     else:
-        warnings.warn('last word is #%d, "%s"' % (n, word))
+        warnings.warn(f'last word is #{n}, {word!r}')
 
 if __name__ == '__main__':
     main()

17-it-generator/sentence_iter2.py

@@ -17,14 +17,14 @@ class Sentence:
         self.text = text
 
     def __repr__(self):
-        return 'Sentence(%s)' % reprlib.repr(self.text)
+        return f'Sentence({reprlib.repr(self.text)})'
 
     def __iter__(self):
         word_iter = RE_WORD.finditer(self.text)  # <1>
         return SentenceIter(word_iter)  # <2>
 
 
-class SentenceIter():
+class SentenceIter:
 
     def __init__(self, word_iter):
         self.word_iter = word_iter  # <3>

17-it-generator/tree/extra/pretty_tree.py

@@ -5,7 +5,7 @@ HLINE = '\u2500'            # ─ BOX DRAWINGS LIGHT HORIZONTAL
 HLINE2 = HLINE * 2
 ELBOW  = f'\u2514{HLINE2} '  # └ BOX DRAWINGS LIGHT UP AND RIGHT
 TEE    = f'\u251C{HLINE2} '  # ├ BOX DRAWINGS LIGHT VERTICAL AND RIGHT
-PIPE  = f'\u2502   '        # │ BOX DRAWINGS LIGHT VERTICAL
+PIPE   = '\u2502   '         # │ BOX DRAWINGS LIGHT VERTICAL
 
 
 def render_lines(tree_iter):

17-it-generator/tree/extra/test_pretty_tree.py

@@ -1,5 +1,3 @@
-import pytest
-
 from pretty_tree import tree, render_lines
 
 def test_1_level():
@@ -99,3 +97,4 @@ def test_4_levels_4_leaves():
 
     result = list(render_lines(tree(A)))
     assert expected == result
+

17-it-generator/tree/step4/test_tree.py

@@ -70,3 +70,4 @@ def test_4_levels_3_leaves():
 
     result = list(tree(A))
     assert expected == result
+

17-it-generator/tree/step5/test_tree.py

@@ -88,3 +88,4 @@ def test_many_levels_1_leaf():
     assert result[0] == ('Root', 0)
     assert result[-1] == ('Sub99', 99)
     assert expected == result
+

17-it-generator/tree/step6/test_tree.py

@@ -88,3 +88,4 @@ def test_many_levels_1_leaf():
     assert result[0] == ('Root', 0)
     assert result[-1] == ('Sub99', 99)
     assert expected == result
+

19-coroutine/taxi_sim.py

@@ -49,11 +49,11 @@ See longer sample run at the end of this module.
 
 """
 
-import random
-import collections
-import queue
 import argparse
-import time
+import collections
+import random
+import queue
+
 
 DEFAULT_NUMBER_OF_TAXIS = 3
 DEFAULT_END_TIME = 180
@@ -126,7 +126,7 @@ def compute_duration(previous_action):
     elif previous_action == 'going home':
         interval = 1
     else:
-        raise ValueError('Unknown previous_action: %s' % previous_action)
+        raise ValueError(f'Unknown previous_action: {previous_action}')
     return int(random.expovariate(1 / interval)) + 1
 
 

19-coroutine/taxi_sim0.py

@@ -27,11 +27,10 @@ See explanation and longer sample run at the end of this module.
 
 """
 
-import sys
+import argparse
-import random
 import collections
 import queue
-import argparse
+import random
 
 DEFAULT_NUMBER_OF_TAXIS = 3
 DEFAULT_END_TIME = 80
@@ -68,7 +67,6 @@ class Simulator:
         self.events = queue.PriorityQueue()
         self.procs = dict(procs_map)
 
-
     def run(self, end_time):  # <1>
         """Schedule and display events until time is up"""
         # schedule the first event for each cab

21-futures/getflags/requirements.txt

@@ -5,7 +5,7 @@ certifi==2020.12.5
 chardet==4.0.0
 idna==2.10
 requests==2.25.1
-urllib3==1.26.4
+urllib3==1.26.3
 tqdm==4.56.2
 multidict==5.1.0
 yarl==1.6.3

22-async/domains/curio/domainlib.py

@@ -1,8 +1,9 @@
-from curio import TaskGroup
-import curio.socket as socket
 from collections.abc import Iterable, AsyncIterator
 from typing import NamedTuple
 
+from curio import TaskGroup
+import curio.socket as socket
+
 
 class Result(NamedTuple):
     domain: str

23-dyn-attr-prop/oscon/schedule_v2.py

@@ -16,8 +16,8 @@ schedule_v2.py: property to get venue linked to an event
 """
 
 # tag::SCHEDULE2_RECORD[]
-import json
 import inspect  # <1>
+import json
 
 JSON_PATH = 'data/osconfeed.json'
 

23-dyn-attr-prop/oscon/schedule_v3.py

@@ -20,8 +20,8 @@ schedule_v3.py: property to get list of event speakers
 # end::SCHEDULE3_DEMO[]
 """
 
-import json
 import inspect
+import json
 
 JSON_PATH = 'data/osconfeed.json'
 

23-dyn-attr-prop/oscon/schedule_v4_hasattr.py

@@ -18,8 +18,8 @@ schedule_v4.py: homegrown cached property for speakers
 # end::SCHEDULE4_DEMO[]
 """
 
-import json
 import inspect
+import json
 
 JSON_PATH = 'data/osconfeed.json'
 

24-descriptor/bulkfood/bulkfood_v4.py

@@ -54,7 +54,7 @@ class Quantity:
             msg = f'{self.storage_name} must be > 0'
             raise ValueError(msg)
 
-    # no __get__ needed
+    # no __get__ needed  # <4>
 
 class LineItem:
     weight = Quantity()  # <5>

24-descriptor/bulkfood/model_v5.py

@@ -32,5 +32,5 @@ class NonBlank(Validated):
         value = value.strip()
         if len(value) == 0:
             raise ValueError(f'{name} cannot be blank')
-        return value  # <8>
+        return value  # <2>
 # end::MODEL_V5_VALIDATED_SUB[]

25-class-metaprog/autoconst/autoconst.py

@@ -0,0 +1,22 @@
+# tag::WilyDict[]
+class WilyDict(dict):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.__next_value = 0
+
+    def __missing__(self, key):
+        if key.startswith('__') and key.endswith('__'):
+            raise KeyError(key)
+        self[key] = value = self.__next_value
+        self.__next_value += 1
+        return value
+# end::WilyDict[]
+
+# tag::AUTOCONST[]
+class AutoConstMeta(type):
+    def __prepare__(name, bases, **kwargs):
+        return WilyDict()
+
+class AutoConst(metaclass=AutoConstMeta):
+    pass
+# end::AUTOCONST[]

25-class-metaprog/autoconst/autoconst_demo.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+"""
+Testing ``WilyDict``::
+
+    >>> from autoconst import WilyDict
+    >>> wd = WilyDict()
+    >>> len(wd)
+    0
+    >>> wd['first']
+    0
+    >>> wd
+    {'first': 0}
+    >>> wd['second']
+    1
+    >>> wd['third']
+    2
+    >>> len(wd)
+    3
+    >>> wd
+    {'first': 0, 'second': 1, 'third': 2}
+    >>> wd['__magic__']
+    Traceback (most recent call last):
+      ...
+    KeyError: '__magic__'
+
+Testing ``AutoConst``::
+
+    >>> from autoconst import AutoConst
+
+# tag::AUTOCONST[]
+    >>> class Flavor(AutoConst):
+    ...     banana
+    ...     coconut
+    ...     vanilla
+    ...
+    >>> Flavor.vanilla
+    2
+    >>> Flavor.banana, Flavor.coconut
+    (0, 1)
+
+# end::AUTOCONST[]
+
+"""
+
+from autoconst import AutoConst
+
+
+class Flavor(AutoConst):
+    banana
+    coconut
+    vanilla
+
+
+print('Flavor.vanilla ==', Flavor.vanilla)

25-class-metaprog/bulkfood/README.md

@@ -0,0 +1,34 @@
+# Legacy Class Descriptor and Metaclass Examples
+
+Examples from _Fluent Python, First Edition_—Chapter 21, _Class Metaprogramming_,
+that are mentioned in _Fluent Python, Second Edition_—Chapter 25, _Class Metaprogramming_.
+
+These examples were developed with Python 3.4.
+They run correctly in Python 3.9, but now it is easier to fullfill the same requirements
+without resorting to class decorators or metaclasses.
+
+I have preserved them here as examples of class metaprogramming techniques
+that you may find in legacy code, and that can be refactored to simpler code
+using a base class with `__init_subclass__` and decorators implementing `__set_name__`.
+
+## Suggested Exercise
+
+If you'd like to practice the concepts presented in chapters 24 and 25 of
+_Fluent Python, Second Edition_,
+you may to refactor the most advanced example, `model_v8.py` with these changes:
+
+1. Simplify the `AutoStorage` descriptor by implementing `__set_name__`.
+This will allow you to simplify the `EntityMeta` metaclass as well.
+
+2. Rewrite the `Entity` class to use `__init_subclass__` instead of the `EntityMeta` metaclass—which you can then delete.
+
+Nothing should change in the `bulkfood_v8.py` code, and its doctests should still pass.
+
+To run the doctests while refactoring, it's often convenient to pass the `-f` option,
+to exit the test runner on the first failing test.
+
+```
+$ python3 -m doctest -f bulkfood_v8.py
+```
+
+Enjoy!

25-class-metaprog/bulkfood/bulkfood_v6.py

@@ -0,0 +1,84 @@
+"""
+
+A line item for a bulk food order has description, weight and price fields::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> raisins.weight, raisins.description, raisins.price
+    (10, 'Golden raisins', 6.95)
+
+A ``subtotal`` method gives the total price for that line item::
+
+    >>> raisins.subtotal()
+    69.5
+
+The weight of a ``LineItem`` must be greater than 0::
+
+    >>> raisins.weight = -20
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+No change was made::
+
+    >>> raisins.weight
+    10
+
+The value of the attributes managed by the descriptors are stored in
+alternate attributes, created by the descriptors in each ``LineItem``
+instance::
+
+# tag::LINEITEM_V6_DEMO[]
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> dir(raisins)[:3]
+    ['_NonBlank#description', '_Quantity#price', '_Quantity#weight']
+    >>> LineItem.description.storage_name
+    '_NonBlank#description'
+    >>> raisins.description
+    'Golden raisins'
+    >>> getattr(raisins, '_NonBlank#description')
+    'Golden raisins'
+
+# end::LINEITEM_V6_DEMO[]
+
+If the descriptor is accessed in the class, the descriptor object is
+returned:
+
+    >>> LineItem.weight  # doctest: +ELLIPSIS
+    <model_v6.Quantity object at 0x...>
+    >>> LineItem.weight.storage_name
+    '_Quantity#weight'
+
+
+The `NonBlank` descriptor prevents empty or blank strings to be used
+for the description:
+
+    >>> br_nuts = LineItem('Brazil Nuts', 10, 34.95)
+    >>> br_nuts.description = ' '
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+    >>> void = LineItem('', 1, 1)
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+
+
+"""
+
+# tag::LINEITEM_V6[]
+import model_v6 as model
+
+@model.entity  # <1>
+class LineItem:
+    description = model.NonBlank()
+    weight = model.Quantity()
+    price = model.Quantity()
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price
+# end::LINEITEM_V6[]

25-class-metaprog/bulkfood/bulkfood_v7.py

@@ -0,0 +1,79 @@
+"""
+
+A line item for a bulk food order has description, weight and price fields::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> raisins.weight, raisins.description, raisins.price
+    (10, 'Golden raisins', 6.95)
+
+A ``subtotal`` method gives the total price for that line item::
+
+    >>> raisins.subtotal()
+    69.5
+
+The weight of a ``LineItem`` must be greater than 0::
+
+    >>> raisins.weight = -20
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+No change was made::
+
+    >>> raisins.weight
+    10
+
+The value of the attributes managed by the descriptors are stored in
+alternate attributes, created by the descriptors in each ``LineItem``
+instance::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> dir(raisins)[:3]
+    ['_NonBlank#description', '_Quantity#price', '_Quantity#weight']
+    >>> LineItem.description.storage_name
+    '_NonBlank#description'
+    >>> raisins.description
+    'Golden raisins'
+    >>> getattr(raisins, '_NonBlank#description')
+    'Golden raisins'
+
+If the descriptor is accessed in the class, the descriptor object is
+returned:
+
+    >>> LineItem.weight  # doctest: +ELLIPSIS
+    <model_v7.Quantity object at 0x...>
+    >>> LineItem.weight.storage_name
+    '_Quantity#weight'
+
+
+The `NonBlank` descriptor prevents empty or blank strings to be used
+for the description:
+
+    >>> br_nuts = LineItem('Brazil Nuts', 10, 34.95)
+    >>> br_nuts.description = ' '
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+    >>> void = LineItem('', 1, 1)
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+
+"""
+
+# tag::LINEITEM_V7[]
+import model_v7 as model
+
+class LineItem(model.Entity):  # <1>
+    description = model.NonBlank()
+    weight = model.Quantity()
+    price = model.Quantity()
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price
+# end::LINEITEM_V7[]

25-class-metaprog/bulkfood/bulkfood_v8.py

@@ -0,0 +1,86 @@
+"""
+
+A line item for a bulk food order has description, weight and price fields::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> raisins.weight, raisins.description, raisins.price
+    (10, 'Golden raisins', 6.95)
+
+A ``subtotal`` method gives the total price for that line item::
+
+    >>> raisins.subtotal()
+    69.5
+
+The weight of a ``LineItem`` must be greater than 0::
+
+    >>> raisins.weight = -20
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+No change was made::
+
+    >>> raisins.weight
+    10
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> dir(raisins)[:3]
+    ['_NonBlank#description', '_Quantity#price', '_Quantity#weight']
+    >>> LineItem.description.storage_name
+    '_NonBlank#description'
+    >>> raisins.description
+    'Golden raisins'
+    >>> getattr(raisins, '_NonBlank#description')
+    'Golden raisins'
+
+If the descriptor is accessed in the class, the descriptor object is
+returned:
+
+    >>> LineItem.weight  # doctest: +ELLIPSIS
+    <model_v8.Quantity object at 0x...>
+    >>> LineItem.weight.storage_name
+    '_Quantity#weight'
+
+
+The `NonBlank` descriptor prevents empty or blank strings to be used
+for the description:
+
+    >>> br_nuts = LineItem('Brazil Nuts', 10, 34.95)
+    >>> br_nuts.description = ' '
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+    >>> void = LineItem('', 1, 1)
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+
+
+Fields can be retrieved in the order they were declared:
+
+# tag::LINEITEM_V8_DEMO[]
+    >>> for name in LineItem.field_names():
+    ...     print(name)
+    ...
+    description
+    weight
+    price
+
+# end::LINEITEM_V8_DEMO[]
+
+"""
+
+import model_v8 as model
+
+class LineItem(model.Entity):
+    description = model.NonBlank()
+    weight = model.Quantity()
+    price = model.Quantity()
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price

25-class-metaprog/bulkfood/model_v6.py

@@ -0,0 +1,60 @@
+import abc
+
+
+class AutoStorage:
+    __counter = 0
+
+    def __init__(self):
+        cls = self.__class__
+        prefix = cls.__name__
+        index = cls.__counter
+        self.storage_name = '_{}#{}'.format(prefix, index)
+        cls.__counter += 1
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+        else:
+            return getattr(instance, self.storage_name)
+
+    def __set__(self, instance, value):
+        setattr(instance, self.storage_name, value)
+
+
+class Validated(abc.ABC, AutoStorage):
+
+    def __set__(self, instance, value):
+        value = self.validate(instance, value)
+        super().__set__(instance, value)
+
+    @abc.abstractmethod
+    def validate(self, instance, value):
+        """return validated value or raise ValueError"""
+
+
+class Quantity(Validated):
+    """a number greater than zero"""
+
+    def validate(self, instance, value):
+        if value <= 0:
+            raise ValueError('value must be > 0')
+        return value
+
+
+class NonBlank(Validated):
+    """a string with at least one non-space character"""
+
+    def validate(self, instance, value):
+        value = value.strip()
+        if len(value) == 0:
+            raise ValueError('value cannot be empty or blank')
+        return value
+
+# tag::MODEL_V6[]
+def entity(cls):  # <1>
+    for key, attr in cls.__dict__.items():  # <2>
+        if isinstance(attr, Validated):  # <3>
+            type_name = type(attr).__name__
+            attr.storage_name = '_{}#{}'.format(type_name, key)  # <4>
+    return cls  # <5>
+# end::MODEL_V6[]

25-class-metaprog/bulkfood/model_v7.py

@@ -0,0 +1,66 @@
+import abc
+
+
+class AutoStorage:
+    __counter = 0
+
+    def __init__(self):
+        cls = self.__class__
+        prefix = cls.__name__
+        index = cls.__counter
+        self.storage_name = '_{}#{}'.format(prefix, index)
+        cls.__counter += 1
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+        else:
+            return getattr(instance, self.storage_name)
+
+    def __set__(self, instance, value):
+        setattr(instance, self.storage_name, value)
+
+
+class Validated(abc.ABC, AutoStorage):
+
+    def __set__(self, instance, value):
+        value = self.validate(instance, value)
+        super().__set__(instance, value)
+
+    @abc.abstractmethod
+    def validate(self, instance, value):
+        """return validated value or raise ValueError"""
+
+
+class Quantity(Validated):
+    """a number greater than zero"""
+
+    def validate(self, instance, value):
+        if value <= 0:
+            raise ValueError('value must be > 0')
+        return value
+
+
+class NonBlank(Validated):
+    """a string with at least one non-space character"""
+
+    def validate(self, instance, value):
+        value = value.strip()
+        if len(value) == 0:
+            raise ValueError('value cannot be empty or blank')
+        return value
+
+# tag::MODEL_V7[]
+class EntityMeta(type):
+    """Metaclass for business entities with validated fields"""
+
+    def __init__(cls, name, bases, attr_dict):
+        super().__init__(name, bases, attr_dict)  # <1>
+        for key, attr in attr_dict.items():  # <2>
+            if isinstance(attr, Validated):
+                type_name = type(attr).__name__
+                attr.storage_name = '_{}#{}'.format(type_name, key)
+
+class Entity(metaclass=EntityMeta):  # <3>
+    """Business entity with validated fields"""
+# end::MODEL_V7[]

25-class-metaprog/bulkfood/model_v8.py

@@ -0,0 +1,80 @@
+import abc
+import collections
+
+
+class AutoStorage:
+    __counter = 0
+
+    def __init__(self):
+        cls = self.__class__
+        prefix = cls.__name__
+        index = cls.__counter
+        self.storage_name = '_{}#{}'.format(prefix, index)
+        cls.__counter += 1
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+        else:
+            return getattr(instance, self.storage_name)
+
+    def __set__(self, instance, value):
+        setattr(instance, self.storage_name, value)
+
+
+class Validated(abc.ABC, AutoStorage):
+
+    def __set__(self, instance, value):
+        value = self.validate(instance, value)
+        super().__set__(instance, value)
+
+    @abc.abstractmethod
+    def validate(self, instance, value):
+        """return validated value or raise ValueError"""
+
+
+class Quantity(Validated):
+    """a number greater than zero"""
+
+    def validate(self, instance, value):
+        if value <= 0:
+            raise ValueError('value must be > 0')
+        return value
+
+
+class NonBlank(Validated):
+    """a string with at least one non-space character"""
+
+    def validate(self, instance, value):
+        value = value.strip()
+        if len(value) == 0:
+            raise ValueError('value cannot be empty or blank')
+        return value
+
+# tag::MODEL_V8[]
+class EntityMeta(type):
+    """Metaclass for business entities with validated fields"""
+
+    @classmethod
+    def __prepare__(cls, name, bases):
+        return collections.OrderedDict()  # <1>
+
+    def __init__(cls, name, bases, attr_dict):
+        super().__init__(name, bases, attr_dict)
+        cls._field_names = []  # <2>
+        for key, attr in attr_dict.items():  # <3>
+            if isinstance(attr, Validated):
+                type_name = type(attr).__name__
+                attr.storage_name = '_{}#{}'.format(type_name, key)
+                cls._field_names.append(key)  # <4>
+
+
+class Entity(metaclass=EntityMeta):
+    """Business entity with validated fields"""
+
+    @classmethod
+    def field_names(cls):  # <5>
+        for name in cls._field_names:
+            yield name
+
+# end::MODEL_V8[]

25-class-metaprog/checked/decorator/checkeddeco.py

@@ -8,13 +8,13 @@ used to create an instance, and provides a nice ``__repr__``::
     ... class Movie:
     ...     title: str
     ...     year: int
-    ...     megabucks: float
+    ...     box_office: float
     ...
-    >>> movie = Movie(title='The Godfather', year=1972, megabucks=137)  # <3>
+    >>> movie = Movie(title='The Godfather', year=1972, box_office=137)
     >>> movie.title
     'The Godfather'
-    >>> movie  # <4>
+    >>> movie
-    Movie(title='The Godfather', year=1972, megabucks=137.0)
+    Movie(title='The Godfather', year=1972, box_office=137.0)
 
 # end::MOVIE_DEFINITION[]
 
@@ -23,14 +23,14 @@ including during instantiation::
 
 # tag::MOVIE_TYPE_VALIDATION[]
 
-    >>> movie.year = 'MCMLXXII'  # <1>
+    >>> blockbuster = Movie(title='Avatar', year=2009, box_office='billions')
+    Traceback (most recent call last):
+      ...
+    TypeError: 'billions' is not compatible with box_office:float
+    >>> movie.year = 'MCMLXXII'
     Traceback (most recent call last):
       ...
     TypeError: 'MCMLXXII' is not compatible with year:int
-    >>> blockbuster = Movie(title='Avatar', year=2009, megabucks='billions')  # <2>
-    Traceback (most recent call last):
-      ...
-    TypeError: 'billions' is not compatible with megabucks:float
 
 # end::MOVIE_TYPE_VALIDATION[]
 
@@ -40,13 +40,13 @@ default values::
 # tag::MOVIE_DEFAULTS[]
 
     >>> Movie(title='Life of Brian')
-    Movie(title='Life of Brian', year=0, megabucks=0.0)
+    Movie(title='Life of Brian', year=0, box_office=0.0)
 
 # end::MOVIE_DEFAULTS[]
 
 Providing extra arguments to the constructor is not allowed::
 
-    >>> blockbuster = Movie(title='Avatar', year=2009, megabucks=2000,
+    >>> blockbuster = Movie(title='Avatar', year=2009, box_office=2000,
     ...                     director='James Cameron')
     Traceback (most recent call last):
       ...
@@ -62,109 +62,90 @@ Creating new attributes at runtime is restricted as well::
 The `_as_dict` instance creates a `dict` from the attributes of a `Movie` object::
 
     >>> movie._asdict()
-    {'title': 'The Godfather', 'year': 1972, 'megabucks': 137.0}
+    {'title': 'The Godfather', 'year': 1972, 'box_office': 137.0}
 
 """
 
 from collections.abc import Callable  # <1>
 from typing import Any, NoReturn, get_type_hints
 
-MISSING = object()  # <2>
-
-
 class Field:
-    def __init__(self, name: str, constructor: Callable) -> None:  # <3>
+    def __init__(self, name: str, constructor: Callable) -> None:  # <2>
+        if not callable(constructor) or constructor is type(None):
+            raise TypeError(f'{name!r} type hint must be callable')
         self.name = name
         self.constructor = constructor
 
-    def __set__(self, instance: Any, value: Any) -> None:  # <4>
+    def __set__(self, instance: Any, value: Any) -> None:  # <3>
-        if value is MISSING:  # <5>
+        if value is ...:  # <4>
             value = self.constructor()
         else:
             try:
-                value = self.constructor(value)  # <6>
+                value = self.constructor(value)  # <5>
             except (TypeError, ValueError) as e:
                 type_name = self.constructor.__name__
                 msg = (
                     f'{value!r} is not compatible with {self.name}:{type_name}'
                 )
                 raise TypeError(msg) from e
-        instance.__dict__[self.name] = value  # <7>
+        instance.__dict__[self.name] = value  # <6>
 
 
-# tag::CHECKED_DECORATOR_TOP[]
+# tag::CHECKED_DECORATOR[]
-_methods_to_inject: list[Callable] = []
+def checked(cls: type) -> type:  # <1>
-_classmethods_to_inject: list[Callable] = []
+    for name, constructor in _fields(cls).items():    # <2>
+        setattr(cls, name, Field(name, constructor))  # <3>
 
-def checked(cls: type) -> type:  # <2>
+    cls._fields = classmethod(_fields)  #type: ignore  # <4>
-    for func in _methods_to_inject:
-        name = func.__name__
-        setattr(cls, name, func)  # <5>
 
-    for func in _classmethods_to_inject:
+    instance_methods = (  # <5>
-        name = func.__name__
+        __init__,
-        setattr(cls, name, classmethod(func))  # <5>
+        __repr__,
+        __setattr__,
+        _asdict,
+        __flag_unknown_attrs,
+    )
+    for method in instance_methods:  # <6>
+        setattr(cls, method.__name__, method)
 
-    for name, constructor in _fields(cls).items():   # <4>
+    return cls  # <7>
-        setattr(cls, name, Field(name, constructor))  # <5>
+# end::CHECKED_DECORATOR[]
 
-    return cls
+# tag::CHECKED_METHODS[]
-
+def _fields(cls: type) -> dict[str, type]:
-
-def _method(func: Callable) -> Callable:
-    _methods_to_inject.append(func)
-    return func
-
-
-def _classmethod(func: Callable) -> Callable:
-    _classmethods_to_inject.append(func)
-    return func
-
-# tag::CHECKED_METHODS_TOP[]
-@_classmethod
-def _fields(cls: type) -> dict[str, type]:  # <1>
     return get_type_hints(cls)
 
-@_method
 def __init__(self: Any, **kwargs: Any) -> None:
-    for name in self._fields():             # <6>
+    for name in self._fields():
-        value = kwargs.pop(name, MISSING)   # <7>
+        value = kwargs.pop(name, ...)
-        setattr(self, name, value)          # <8>
+        setattr(self, name, value)
-    if kwargs:                              # <9>
+    if kwargs:
-        self.__flag_unknown_attrs(*kwargs)  # <10>
+        self.__flag_unknown_attrs(*kwargs)
 
-@_method
+def __setattr__(self: Any, name: str, value: Any) -> None:
-def __setattr__(self: Any, name: str, value: Any) -> None:  # <11>
+    if name in self._fields():
-    if name in self._fields():              # <12>
         cls = self.__class__
         descriptor = getattr(cls, name)
-        descriptor.__set__(self, value)     # <13>
+        descriptor.__set__(self, value)
-    else:                                   # <14>
+    else:
         self.__flag_unknown_attrs(name)
-# end::CHECKED_METHODS_TOP[]
 
-# tag::CHECKED_METHODS_BOTTOM[]
+def __flag_unknown_attrs(self: Any, *names: str) -> NoReturn:
-@_method
-def __flag_unknown_attrs(self: Any, *names: str) -> NoReturn:  # <1>
     plural = 's' if len(names) > 1 else ''
     extra = ', '.join(f'{name!r}' for name in names)
     cls_name = repr(self.__class__.__name__)
     raise AttributeError(f'{cls_name} has no attribute{plural} {extra}')
 
-
+def _asdict(self: Any) -> dict[str, Any]:
-@_method
-def _asdict(self: Any) -> dict[str, Any]:  # <2>
     return {
         name: getattr(self, name)
         for name, attr in self.__class__.__dict__.items()
         if isinstance(attr, Field)
     }
 
-
+def __repr__(self: Any) -> str:
-@_method
-def __repr__(self: Any) -> str:  # <3>
     kwargs = ', '.join(
         f'{key}={value!r}' for key, value in self._asdict().items()
     )
     return f'{self.__class__.__name__}({kwargs})'
-# end::CHECKED_METHODS_BOTTOM[]
+# end::CHECKED_METHODS[]

25-class-metaprog/checked/decorator/checkeddeco_demo.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+
+from checkeddeco import checked
+
+@checked
+class Movie:
+    title: str
+    year: int
+    box_office: float
+
+
+if __name__ == '__main__':
+    # No static type checker can understand this...
+    movie = Movie(title='The Godfather', year=1972, box_office=137)  # type: ignore
+    print(movie.title)
+    print(movie)
+    try:
+        # remove the "type: ignore" comment to see Mypy correctly spot the error
+        movie.year = 'MCMLXXII'  # type: ignore
+    except TypeError as e:
+        print(e)
+    try:
+        # Again, no static type checker can understand this...
+        blockbuster = Movie(title='Avatar', year=2009, box_office='billions')  # type: ignore
+    except TypeError as e:
+        print(e)

25-class-metaprog/checked/decorator/checkeddeco_test.py

@@ -38,3 +38,13 @@ def test_constructor_attribute_error():
         felix = Cat(name='Felix', weight=3.2, age=7)
 
     assert str(e.value) == "'Cat' has no attribute 'age'"
+
+
+def test_field_invalid_constructor():
+    with pytest.raises(TypeError) as e:
+        @checked
+        class Cat:
+            name: str
+            weight: None
+
+    assert str(e.value) == "'weight' type hint must be callable"

25-class-metaprog/checked/initsub/checked_demo.py

@@ -1,13 +1,15 @@
+#!/usr/bin/env python3
+
 from checkedlib import Checked
 
 class Movie(Checked):
     title: str
     year: int
-    megabucks: float
+    box_office: float
 
 
 if __name__ == '__main__':
-    movie = Movie(title='The Godfather', year=1972, megabucks=137)
+    movie = Movie(title='The Godfather', year=1972, box_office=137)
     print(movie.title)
     print(movie)
     try:
@@ -16,6 +18,6 @@ if __name__ == '__main__':
     except TypeError as e:
         print(e)
     try:
-        blockbuster = Movie(title='Avatar', year=2009, megabucks='billions')
+        blockbuster = Movie(title='Avatar', year=2009, box_office='billions')
     except TypeError as e:
         print(e)

25-class-metaprog/checked/initsub/checkedlib.py

@@ -7,29 +7,29 @@ used to create an instance, and provides a nice ``__repr__``::
     >>> class Movie(Checked):  # <1>
     ...     title: str  # <2>
     ...     year: int
-    ...     megabucks: float
+    ...     box_office: float
     ...
-    >>> movie = Movie(title='The Godfather', year=1972, megabucks=137)  # <3>
+    >>> movie = Movie(title='The Godfather', year=1972, box_office=137)  # <3>
     >>> movie.title
     'The Godfather'
     >>> movie  # <4>
-    Movie(title='The Godfather', year=1972, megabucks=137.0)
+    Movie(title='The Godfather', year=1972, box_office=137.0)
 
 # end::MOVIE_DEFINITION[]
 
-The type of arguments is runtime checked when an attribute is set,
+The type of arguments is runtime checked during instantiation
-including during instantiation::
+and when an attribute is set::
 
 # tag::MOVIE_TYPE_VALIDATION[]
 
-    >>> movie.year = 'MCMLXXII'  # <1>
+    >>> blockbuster = Movie(title='Avatar', year=2009, box_office='billions')
+    Traceback (most recent call last):
+      ...
+    TypeError: 'billions' is not compatible with box_office:float
+    >>> movie.year = 'MCMLXXII'
     Traceback (most recent call last):
       ...
     TypeError: 'MCMLXXII' is not compatible with year:int
-    >>> blockbuster = Movie(title='Avatar', year=2009, megabucks='billions')  # <2>
-    Traceback (most recent call last):
-      ...
-    TypeError: 'billions' is not compatible with megabucks:float
 
 # end::MOVIE_TYPE_VALIDATION[]
 
@@ -39,29 +39,29 @@ default values::
 # tag::MOVIE_DEFAULTS[]
 
     >>> Movie(title='Life of Brian')
-    Movie(title='Life of Brian', year=0, megabucks=0.0)
+    Movie(title='Life of Brian', year=0, box_office=0.0)
 
 # end::MOVIE_DEFAULTS[]
 
 Providing extra arguments to the constructor is not allowed::
 
-    >>> blockbuster = Movie(title='Avatar', year=2009, megabucks=2000,
+    >>> blockbuster = Movie(title='Avatar', year=2009, box_office=2000,
     ...                     director='James Cameron')
     Traceback (most recent call last):
       ...
-    AttributeError: 'Movie' has no attribute 'director'
+    AttributeError: 'Movie' object has no attribute 'director'
 
 Creating new attributes at runtime is restricted as well::
 
     >>> movie.director = 'Francis Ford Coppola'
     Traceback (most recent call last):
       ...
-    AttributeError: 'Movie' has no attribute 'director'
+    AttributeError: 'Movie' object has no attribute 'director'
 
 The `_as_dict` instance creates a `dict` from the attributes of a `Movie` object::
 
     >>> movie._asdict()
-    {'title': 'The Godfather', 'year': 1972, 'megabucks': 137.0}
+    {'title': 'The Godfather', 'year': 1972, 'box_office': 137.0}
 
 """
 
@@ -69,27 +69,25 @@ The `_as_dict` instance creates a `dict` from the attributes of a `Movie` object
 from collections.abc import Callable  # <1>
 from typing import Any, NoReturn, get_type_hints
 
-MISSING = object()  # <2>
-
 
 class Field:
-    def __init__(self, name: str, constructor: Callable) -> None:  # <3>
+    def __init__(self, name: str, constructor: Callable) -> None:  # <2>
+        if not callable(constructor) or constructor is type(None):  # <3>
+            raise TypeError(f'{name!r} type hint must be callable')
         self.name = name
         self.constructor = constructor
 
-    def __set__(self, instance: 'Checked', value: Any) -> None:  # <4>
+    def __set__(self, instance: Any, value: Any) -> None:
-        if value is MISSING:  # <5>
+        if value is ...:  # <4>
             value = self.constructor()
         else:
             try:
-                value = self.constructor(value)  # <6>
+                value = self.constructor(value)  # <5>
-            except (TypeError, ValueError) as e:
+            except (TypeError, ValueError) as e:  # <6>
                 type_name = self.constructor.__name__
                 msg = f'{value!r} is not compatible with {self.name}:{type_name}'
                 raise TypeError(msg) from e
         instance.__dict__[self.name] = value  # <7>
-
-
 # end::CHECKED_FIELD[]
 
 # tag::CHECKED_TOP[]
@@ -105,36 +103,36 @@ class Checked:
 
     def __init__(self, **kwargs: Any) -> None:
         for name in self._fields():             # <6>
-            value = kwargs.pop(name, MISSING)   # <7>
+            value = kwargs.pop(name, ...)       # <7>
             setattr(self, name, value)          # <8>
         if kwargs:                              # <9>
             self.__flag_unknown_attrs(*kwargs)  # <10>
 
-    def __setattr__(self, name: str, value: Any) -> None:  # <11>
-        if name in self._fields():              # <12>
-            cls = self.__class__
-            descriptor = getattr(cls, name)
-            descriptor.__set__(self, value)     # <13>
-        else:                                   # <14>
-            self.__flag_unknown_attrs(name)
-
     # end::CHECKED_TOP[]
 
     # tag::CHECKED_BOTTOM[]
-    def __flag_unknown_attrs(self, *names: str) -> NoReturn:  # <1>
+    def __setattr__(self, name: str, value: Any) -> None:  # <1>
+        if name in self._fields():              # <2>
+            cls = self.__class__
+            descriptor = getattr(cls, name)
+            descriptor.__set__(self, value)     # <3>
+        else:                                   # <4>
+            self.__flag_unknown_attrs(name)
+
+    def __flag_unknown_attrs(self, *names: str) -> NoReturn:  # <5>
         plural = 's' if len(names) > 1 else ''
         extra = ', '.join(f'{name!r}' for name in names)
         cls_name = repr(self.__class__.__name__)
-        raise AttributeError(f'{cls_name} has no attribute{plural} {extra}')
+        raise AttributeError(f'{cls_name} object has no attribute{plural} {extra}')
 
-    def _asdict(self) -> dict[str, Any]:  # <2>
+    def _asdict(self) -> dict[str, Any]:  # <6>
         return {
             name: getattr(self, name)
             for name, attr in self.__class__.__dict__.items()
             if isinstance(attr, Field)
         }
 
-    def __repr__(self) -> str:  # <3>
+    def __repr__(self) -> str:  # <7>
         kwargs = ', '.join(
             f'{key}={value!r}' for key, value in self._asdict().items()
         )

25-class-metaprog/checked/initsub/checkedlib_test.py

@@ -0,0 +1,59 @@
+import pytest
+
+
+from checkedlib import Checked
+
+
+def test_field_validation_type_error():
+    class Cat(Checked):
+        name: str
+        weight: float
+
+    with pytest.raises(TypeError) as e:
+        felix = Cat(name='Felix', weight=None)
+
+    assert str(e.value) == 'None is not compatible with weight:float'
+
+
+def test_field_validation_value_error():
+    class Cat(Checked):
+        name: str
+        weight: float
+
+    with pytest.raises(TypeError) as e:
+        felix = Cat(name='Felix', weight='half stone')
+
+    assert str(e.value) == "'half stone' is not compatible with weight:float"
+
+
+def test_constructor_attribute_error():
+    class Cat(Checked):
+        name: str
+        weight: float
+
+    with pytest.raises(AttributeError) as e:
+        felix = Cat(name='Felix', weight=3.2, age=7)
+
+    assert str(e.value) == "'Cat' object has no attribute 'age'"
+
+
+def test_assignment_attribute_error():
+    class Cat(Checked):
+        name: str
+        weight: float
+
+    felix = Cat(name='Felix', weight=3.2)
+    with pytest.raises(AttributeError) as e:
+        felix.color = 'tan'
+
+    assert str(e.value) == "'Cat' object has no attribute 'color'"
+
+
+def test_field_invalid_constructor():
+    with pytest.raises(TypeError) as e:
+        class Cat(Checked):
+            name: str
+            weight: None
+
+    assert str(e.value) == "'weight' type hint must be callable"
+

25-class-metaprog/checked/metaclass/checked_demo.py

@@ -1,22 +1,25 @@
-from checkeddeco import checked
+#!/usr/bin/env python3
 
-@checked
+# tag::MOVIE_DEMO[]
-class Movie:
+from checkedlib import Checked
+
+class Movie(Checked):
     title: str
     year: int
-    megabucks: float
+    box_office: float
-
 
 if __name__ == '__main__':
-    movie = Movie(title='The Godfather', year=1972, megabucks=137)
+    movie = Movie(title='The Godfather', year=1972, box_office=137)
-    print(movie.title)
     print(movie)
+    print(movie.title)
+    # end::MOVIE_DEMO[]
+
     try:
         # remove the "type: ignore" comment to see Mypy error
         movie.year = 'MCMLXXII'  # type: ignore
     except TypeError as e:
         print(e)
     try:
-        blockbuster = Movie(title='Avatar', year=2009, megabucks='billions')
+        blockbuster = Movie(title='Avatar', year=2009, box_office='billions')
     except TypeError as e:
         print(e)

25-class-metaprog/checked/metaclass/checkedlib.py

@@ -0,0 +1,148 @@
+"""
+A ``Checked`` subclass definition requires that keyword arguments are
+used to create an instance, and provides a nice ``__repr__``::
+
+# tag::MOVIE_DEFINITION[]
+
+    >>> class Movie(Checked):  # <1>
+    ...     title: str  # <2>
+    ...     year: int
+    ...     box_office: float
+    ...
+    >>> movie = Movie(title='The Godfather', year=1972, box_office=137)  # <3>
+    >>> movie.title
+    'The Godfather'
+    >>> movie  # <4>
+    Movie(title='The Godfather', year=1972, box_office=137.0)
+
+# end::MOVIE_DEFINITION[]
+
+The type of arguments is runtime checked during instantiation
+and when an attribute is set::
+
+# tag::MOVIE_TYPE_VALIDATION[]
+
+    >>> blockbuster = Movie(title='Avatar', year=2009, box_office='billions')
+    Traceback (most recent call last):
+      ...
+    TypeError: 'billions' is not compatible with box_office:float
+    >>> movie.year = 'MCMLXXII'
+    Traceback (most recent call last):
+      ...
+    TypeError: 'MCMLXXII' is not compatible with year:int
+
+# end::MOVIE_TYPE_VALIDATION[]
+
+Attributes not passed as arguments to the constructor are initialized with
+default values::
+
+# tag::MOVIE_DEFAULTS[]
+
+    >>> Movie(title='Life of Brian')
+    Movie(title='Life of Brian', year=0, box_office=0.0)
+
+# end::MOVIE_DEFAULTS[]
+
+Providing extra arguments to the constructor is not allowed::
+
+    >>> blockbuster = Movie(title='Avatar', year=2009, box_office=2000,
+    ...                     director='James Cameron')
+    Traceback (most recent call last):
+      ...
+    AttributeError: 'Movie' object has no attribute 'director'
+
+Creating new attributes at runtime is restricted as well::
+
+    >>> movie.director = 'Francis Ford Coppola'
+    Traceback (most recent call last):
+      ...
+    AttributeError: 'Movie' object has no attribute 'director'
+
+The `_as_dict` instance creates a `dict` from the attributes of a `Movie` object::
+
+    >>> movie._asdict()
+    {'title': 'The Godfather', 'year': 1972, 'box_office': 137.0}
+
+"""
+
+from collections.abc import Callable
+from typing import Any, NoReturn, get_type_hints
+
+# tag::CHECKED_FIELD[]
+class Field:
+    def __init__(self, name: str, constructor: Callable) -> None:
+        if not callable(constructor) or constructor is type(None):
+            raise TypeError(f'{name!r} type hint must be callable')
+        self.name = name
+        self.storage_name = '_' + name  # <1>
+        self.constructor = constructor
+
+    def __get__(self, instance, owner=None):  # <2>
+        return getattr(instance, self.storage_name)  # <3>
+
+    def __set__(self, instance: Any, value: Any) -> None:
+        if value is ...:
+            value = self.constructor()
+        else:
+            try:
+                value = self.constructor(value)
+            except (TypeError, ValueError) as e:
+                type_name = self.constructor.__name__
+                msg = f'{value!r} is not compatible with {self.name}:{type_name}'
+                raise TypeError(msg) from e
+        setattr(instance, self.storage_name, value)  # <4>
+# end::CHECKED_FIELD[]
+
+# tag::CHECKED_META[]
+class CheckedMeta(type):
+
+    def __new__(meta_cls, cls_name, bases, cls_dict):  # <1>
+        if '__slots__' not in cls_dict:  # <2>
+            slots = []
+            type_hints = cls_dict.get('__annotations__', {})  # <3>
+            for name, constructor in type_hints.items():   # <4>
+                field = Field(name, constructor)  # <5>
+                cls_dict[name] = field  # <6>
+                slots.append(field.storage_name)  # <7>
+
+            cls_dict['__slots__'] = slots  # <8>
+
+        return super().__new__(
+                meta_cls, cls_name, bases, cls_dict)  # <9>
+# end::CHECKED_META[]
+
+# tag::CHECKED_CLASS[]
+class Checked(metaclass=CheckedMeta):
+    __slots__ = ()  # skip CheckedMeta.__new__ processing
+
+    @classmethod
+    def _fields(cls) -> dict[str, type]:
+        return get_type_hints(cls)
+
+    def __init__(self, **kwargs: Any) -> None:
+        for name in self._fields():
+            value = kwargs.pop(name, ...)
+            setattr(self, name, value)
+        if kwargs:
+            self.__flag_unknown_attrs(*kwargs)
+
+    def __flag_unknown_attrs(self, *names: str) -> NoReturn:
+        plural = 's' if len(names) > 1 else ''
+        extra = ', '.join(f'{name!r}' for name in names)
+        cls_name = repr(self.__class__.__name__)
+        raise AttributeError(f'{cls_name} object has no attribute{plural} {extra}')
+
+    def _asdict(self) -> dict[str, Any]:
+        return {
+            name: getattr(self, name)
+            for name, attr in self.__class__.__dict__.items()
+            if isinstance(attr, Field)
+        }
+
+    def __repr__(self) -> str:
+        kwargs = ', '.join(
+            f'{key}={value!r}' for key, value in self._asdict().items()
+        )
+        return f'{self.__class__.__name__}({kwargs})'
+
+# end::CHECKED_CLASS[]

25-class-metaprog/checked/metaclass/checkedlib_test.py

@@ -34,4 +34,25 @@ def test_constructor_attribute_error():
     with pytest.raises(AttributeError) as e:
         felix = Cat(name='Felix', weight=3.2, age=7)
 
-    assert str(e.value) == "'Cat' has no attribute 'age'"
+    assert str(e.value) == "'Cat' object has no attribute 'age'"
+
+
+def test_assignment_attribute_error():
+    class Cat(Checked):
+        name: str
+        weight: float
+
+    felix = Cat(name='Felix', weight=3.2)
+    with pytest.raises(AttributeError) as e:
+        felix.color = 'tan'
+
+    assert str(e.value) == "'Cat' object has no attribute 'color'"
+
+
+def test_field_invalid_constructor():
+    with pytest.raises(TypeError) as e:
+        class Cat(Checked):
+            name: str
+            weight: None
+
+    assert str(e.value) == "'weight' type hint must be callable"

25-class-metaprog/evalsupport.py

@@ -1,29 +0,0 @@
-# tag::BEGINNING[]
-print('<[100]> evalsupport module start')
-
-def deco_alpha(cls):
-    print('<[200]> deco_alpha')
-
-    def inner_1(self):
-        print('<[300]> deco_alpha:inner_1')
-
-    cls.method_y = inner_1
-    return cls
-
-# end::BEGINNING[]
-# tag::META_ALEPH[]
-class MetaAleph(type):
-    print('<[400]> MetaAleph body')
-
-    def __init__(cls, name, bases, dic):
-        print('<[500]> MetaAleph.__init__')
-
-        def inner_2(self):
-            print('<[600]> MetaAleph.__init__:inner_2')
-
-        cls.method_z = inner_2
-
-# end::META_ALEPH[]
-# tag::END[]
-print('<[700]> evalsupport module end')
-# end::END[]

25-class-metaprog/evaltime.py

@@ -1,49 +0,0 @@
-from evalsupport import deco_alpha
-
-print('<[1]> evaltime module start')
-
-
-class ClassOne():
-    print('<[2]> ClassOne body')
-
-    def __init__(self):
-        print('<[3]> ClassOne.__init__')
-
-    def __del__(self):
-        print('<[4]> ClassOne.__del__')
-
-    def method_x(self):
-        print('<[5]> ClassOne.method_x')
-
-    class ClassTwo(object):
-        print('<[6]> ClassTwo body')
-
-
-@deco_alpha
-class ClassThree():
-    print('<[7]> ClassThree body')
-
-    def method_y(self):
-        print('<[8]> ClassThree.method_y')
-
-
-class ClassFour(ClassThree):
-    print('<[9]> ClassFour body')
-
-    def method_y(self):
-        print('<[10]> ClassFour.method_y')
-
-
-if __name__ == '__main__':
-    print('<[11]> ClassOne tests', 30 * '.')
-    one = ClassOne()
-    one.method_x()
-    print('<[12]> ClassThree tests', 30 * '.')
-    three = ClassThree()
-    three.method_y()
-    print('<[13]> ClassFour tests', 30 * '.')
-    four = ClassFour()
-    four.method_y()
-
-
-print('<[14]> evaltime module end')

25-class-metaprog/evaltime/builderlib.py

@@ -0,0 +1,50 @@
+# tag::BUILDERLIB_TOP[]
+print('@ builderlib module start')
+
+class Builder:  # <1>
+    print('@ Builder body')
+
+    def __init_subclass__(cls):  # <2>
+        print(f'@ Builder.__init_subclass__({cls!r})')
+
+        def inner_0(self):  # <3>
+            print(f'@ SuperA.__init_subclass__:inner_0({self!r})')
+
+        cls.method_a = inner_0
+
+    def __init__(self):
+        super().__init__()
+        print(f'@ Builder.__init__({self!r})')
+
+
+def deco(cls):  # <4>
+    print(f'@ deco({cls!r})')
+
+    def inner_1(self):  # <5>
+        print(f'@ deco:inner_1({self!r})')
+
+    cls.method_b = inner_1
+    return cls  # <6>
+# end::BUILDERLIB_TOP[]
+
+# tag::BUILDERLIB_BOTTOM[]
+class Descriptor:  # <1>
+    print('@ Descriptor body')
+
+    def __init__(self):  # <2>
+        print(f'@ Descriptor.__init__({self!r})')
+
+    def __set_name__(self, owner, name):  # <3>
+        args = (self, owner, name)
+        print(f'@ Descriptor.__set_name__{args!r}')
+
+    def __set__(self, instance, value):  # <4>
+        args = (self, instance, value)
+        print(f'@ Descriptor.__set__{args!r}')
+
+    def __repr__(self):
+        return '<Descriptor instance>'
+
+
+print('@ builderlib module end')
+# end::BUILDERLIB_BOTTOM[]

25-class-metaprog/evaltime/evaldemo.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+
+from builderlib import Builder, deco, Descriptor
+
+print('# evaldemo module start')
+
+@deco  # <1>
+class Klass(Builder):  # <2>
+    print('# Klass body')
+
+    attr = Descriptor()  # <3>
+
+    def __init__(self):
+        super().__init__()
+        print(f'# Klass.__init__({self!r})')
+
+    def __repr__(self):
+        return '<Klass instance>'
+
+
+def main():  # <4>
+    obj = Klass()
+    obj.method_a()
+    obj.method_b()
+    obj.attr = 999
+
+if __name__ == '__main__':
+    main()
+
+print('# evaldemo module end')

25-class-metaprog/evaltime/evaldemo_meta.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+from builderlib import Builder, deco, Descriptor
+from metalib import MetaKlass  # <1>
+
+print('# evaldemo_meta module start')
+
+@deco
+class Klass(Builder, metaclass=MetaKlass):  # <2>
+    print('# Klass body')
+
+    attr = Descriptor()
+
+    def __init__(self):
+        super().__init__()
+        print(f'# Klass.__init__({self!r})')
+
+    def __repr__(self):
+        return '<Klass instance>'
+
+
+def main():
+    obj = Klass()
+    obj.method_a()
+    obj.method_b()
+    obj.method_c()  # <3>
+    obj.attr = 999
+
+
+if __name__ == '__main__':
+    main()
+
+print('# evaldemo_meta module end')

25-class-metaprog/evaltime/metalib.py

@@ -0,0 +1,43 @@
+# tag::METALIB_TOP[]
+print('% metalib module start')
+
+import collections
+
+class NosyDict(collections.UserDict):
+    def __setitem__(self, key, value):
+        args = (self, key, value)
+        print(f'% NosyDict.__setitem__{args!r}')
+        super().__setitem__(key, value)
+
+    def __repr__(self):
+        return '<NosyDict instance>'
+# end::METALIB_TOP[]
+
+# tag::METALIB_BOTTOM[]
+class MetaKlass(type):
+    print('% MetaKlass body')
+
+    @classmethod  # <1>
+    def __prepare__(meta_cls, cls_name, bases):  # <2>
+        args = (meta_cls, cls_name, bases)
+        print(f'% MetaKlass.__prepare__{args!r}')
+        return NosyDict()  # <3>
+
+    def __new__(meta_cls, cls_name, bases, cls_dict):  # <4>
+        args = (meta_cls, cls_name, bases, cls_dict)
+        print(f'% MetaKlass.__new__{args!r}')
+        def inner_2(self):
+            print(f'% MetaKlass.__new__:inner_2({self!r})')
+
+        cls = super().__new__(meta_cls, cls_name, bases, cls_dict.data)  # <5>
+
+        cls.method_c = inner_2  # <6>
+
+        return cls  # <7>
+
+    def __repr__(cls):  # <8>
+        cls_name = cls.__name__
+        return f"<class {cls_name!r} built by MetaKlass>"
+
+print('% metalib module end')
+# end::METALIB_BOTTOM[]

25-class-metaprog/evaltime_meta.py

@@ -1,53 +0,0 @@
-from evalsupport import deco_alpha
-from evalsupport import MetaAleph
-
-print('<[1]> evaltime_meta module start')
-
-
-@deco_alpha
-class ClassThree():
-    print('<[2]> ClassThree body')
-
-    def method_y(self):
-        print('<[3]> ClassThree.method_y')
-
-
-class ClassFour(ClassThree):
-    print('<[4]> ClassFour body')
-
-    def method_y(self):
-        print('<[5]> ClassFour.method_y')
-
-
-class ClassFive(metaclass=MetaAleph):
-    print('<[6]> ClassFive body')
-
-    def __init__(self):
-        print('<[7]> ClassFive.__init__')
-
-    def method_z(self):
-        print('<[8]> ClassFive.method_z')
-
-
-class ClassSix(ClassFive):
-    print('<[9]> ClassSix body')
-
-    def method_z(self):
-        print('<[10]> ClassSix.method_z')
-
-
-if __name__ == '__main__':
-    print('<[11]> ClassThree tests', 30 * '.')
-    three = ClassThree()
-    three.method_y()
-    print('<[12]> ClassFour tests', 30 * '.')
-    four = ClassFour()
-    four.method_y()
-    print('<[13]> ClassFive tests', 30 * '.')
-    five = ClassFive()
-    five.method_z()
-    print('<[14]> ClassSix tests', 30 * '.')
-    six = ClassSix()
-    six.method_z()
-
-print('<[15]> evaltime_meta module end')

25-class-metaprog/factories.py

@@ -27,35 +27,48 @@ The factory also accepts a list or tuple of identifiers:
 
 """
 
-# tag::RECORD_FACTORY[]
-def record_factory(cls_name, field_names):
-    try:
-        field_names = field_names.replace(',', ' ').split()  # <1>
-    except AttributeError:  # no .replace or .split
-        pass  # assume it's already a sequence of strings
-    field_names = tuple(field_names)  # <2>
-    if not all(s.isidentifier() for s in field_names):
-        raise ValueError('field_names must all be valid identifiers')
 
-    def __init__(self, *args, **kwargs):  # <3>
+# tag::RECORD_FACTORY[]
+from typing import Union, Any
+from collections.abc import Iterable, Iterator
+
+FieldNames = Union[str, Iterable[str]]  # <1>
+
+def record_factory(cls_name: str, field_names: FieldNames) -> type[tuple]:  # <2>
+
+    slots = parse_identifiers(field_names)  # <3>
+
+    def __init__(self, *args, **kwargs) -> None:  # <4>
         attrs = dict(zip(self.__slots__, args))
         attrs.update(kwargs)
         for name, value in attrs.items():
             setattr(self, name, value)
 
-    def __iter__(self):  # <4>
+    def __iter__(self) -> Iterator[Any]:  # <5>
         for name in self.__slots__:
             yield getattr(self, name)
 
-    def __repr__(self):  # <5>
+    def __repr__(self):  # <6>
-        values = ', '.join('{}={!r}'.format(*i) for i
+        values = ', '.join(
-                           in zip(self.__slots__, self))
+            '{}={!r}'.format(*i) for i in zip(self.__slots__, self)
-        return '{}({})'.format(self.__class__.__name__, values)
+        )
+        cls_name = self.__class__.__name__
+        return f'{cls_name}({values})'
 
-    cls_attrs = dict(__slots__ = field_names,  # <6>
+    cls_attrs = dict(  # <7>
+        __slots__=slots,
         __init__=__init__,
         __iter__=__iter__,
-                     __repr__  = __repr__)
+        __repr__=__repr__,
+    )
 
-    return type(cls_name, (object,), cls_attrs)  # <7>
+    return type(cls_name, (object,), cls_attrs)  # <8>
+
+
+def parse_identifiers(names: FieldNames) -> tuple[str, ...]:
+    if isinstance(names, str):
+        names = names.replace(',', ' ').split()  # <9>
+    if not all(s.isidentifier() for s in names):
+        raise ValueError('names must all be valid identifiers')
+    return tuple(names)
 # end::RECORD_FACTORY[]

25-class-metaprog/factories_ducktyped.py

@@ -0,0 +1,79 @@
+"""
+record_factory: create simple classes just for holding data fields
+
+# tag::RECORD_FACTORY_DEMO[]
+    >>> Dog = record_factory('Dog', 'name weight owner')  # <1>
+    >>> rex = Dog('Rex', 30, 'Bob')
+    >>> rex  # <2>
+    Dog(name='Rex', weight=30, owner='Bob')
+    >>> name, weight, _ = rex  # <3>
+    >>> name, weight
+    ('Rex', 30)
+    >>> "{2}'s dog weighs {1}kg".format(*rex)  # <4>
+    "Bob's dog weighs 30kg"
+    >>> rex.weight = 32  # <5>
+    >>> rex
+    Dog(name='Rex', weight=32, owner='Bob')
+    >>> Dog.__mro__  # <6>
+    (<class 'factories_ducktyped.Dog'>, <class 'object'>)
+
+# end::RECORD_FACTORY_DEMO[]
+
+The factory also accepts a list or tuple of identifiers:
+
+    >>> Dog = record_factory('Dog', ['name', 'weight', 'owner'])
+    >>> Dog.__slots__
+    ('name', 'weight', 'owner')
+
+"""
+
+
+# tag::RECORD_FACTORY[]
+from typing import Union, Any
+from collections.abc import Sequence, Iterator
+
+FieldNames = Union[str, Sequence[str]]
+
+
+def parse_identifiers(names):
+    try:
+        names = names.replace(',', ' ').split()  # <1>
+    except AttributeError:  # no .replace or .split
+        pass  # assume it's already a sequence of strings
+    if not all(s.isidentifier() for s in names):
+        raise ValueError('names must all be valid identifiers')
+    return tuple(names)
+
+
+def record_factory(cls_name, field_names):
+
+    field_identifiers = parse_identifiers(field_names)
+
+    def __init__(self, *args, **kwargs) -> None:  # <4>
+        attrs = dict(zip(self.__slots__, args))
+        attrs.update(kwargs)
+        for name, value in attrs.items():
+            setattr(self, name, value)
+
+    def __iter__(self) -> Iterator[Any]:  # <5>
+        for name in self.__slots__:
+            yield getattr(self, name)
+
+    def __repr__(self):  # <6>
+        values = ', '.join(
+            '{}={!r}'.format(*i) for i in zip(self.__slots__, self)
+        )
+        cls_name = self.__class__.__name__
+        return f'{cls_name}({values})'
+
+    cls_attrs = dict(
+        __slots__=field_identifiers,  # <7>
+        __init__=__init__,
+        __iter__=__iter__,
+        __repr__=__repr__,
+    )
+
+    return type(cls_name, (object,), cls_attrs)  # <8>
+
+
+# end::RECORD_FACTORY[]

25-class-metaprog/hours/hours.py

@@ -0,0 +1,115 @@
+"""
+Abusing ``__class_getitem__`` to make a nano-DSL for working
+with hours, minutes, and seconds--these last two in base 60.
+
+``H`` is an alias for the ``Hours`` class::
+
+    >>> H[1]
+    1:00
+    >>> H[1:30]
+    1:30
+    >>> H[1::5]
+    1:00:05
+    >>> H[::5]
+    0:00:05
+
+An ``H`` instance can be converted to a float number of hours::
+
+    >>> float(H[1:15])
+    1.25
+    >>> float(H[1:30:30])  # doctest: +ELLIPSIS
+    1.5083333...
+    >>> float(H[1::5])     # doctest: +ELLIPSIS
+    1.0013888...
+
+The ``H`` constructor accepts hours, minutes, and/or seconds::
+
+    >>> H(1.5)
+    1:30
+    >>> H(1.9)
+    1:54
+    >>> H(1, 30, 30)
+    1:30:30
+    >>> H(s = 7205)
+    2:00:05
+    >>> H(1/3)
+    0:20
+    >>> H(1/1000)
+    0:00:03.6
+
+An ``H`` instance is iterable, for convenient unpacking::
+
+    >>> hms = H[1:22:33]
+    >>> h, m, s = hms
+    >>> h, m, s
+    (1, 22, 33)
+    >>> tuple(hms)
+    (1, 22, 33)
+
+
+``H`` instances can be added::
+
+    >>> H[1:45:12] + H[2:15:50]
+    4:01:02
+"""
+
+from typing import Tuple, Union
+
+
+def normalize(s: float) -> Tuple[int, int, float]:
+    h, r = divmod(s, 3600)
+    m, s = divmod(r, 60)
+    return int(h), int(m), s
+
+
+def valid_base_60(n, unit):
+    if not (0 <= n < 60):
+        raise ValueError(f'invalid {unit} {n}')
+    return n
+
+
+class Hours:
+    h: int
+    _m: int
+    _s: float
+
+    def __class_getitem__(cls, parts: Union[slice, float]) -> 'Hours':
+        if isinstance(parts, slice):
+            h = parts.start or 0
+            m = valid_base_60(parts.stop or 0, 'minutes')
+            s = valid_base_60(parts.step or 0, 'seconds')
+        else:
+            h, m, s = normalize(parts * 3600)
+        return Hours(h, m, s)
+
+    def __init__(self, h: float = 0, m: float = 0, s: float = 0):
+        if h < 0 or m < 0 or s < 0:
+            raise ValueError('invalid negative argument')
+        self.h, self.m, self.s = normalize(h * 3600 + m * 60 + s)
+
+    def __repr__(self):
+        h, m, s = self
+        display_s = f'{s:06.3f}'
+        display_s = display_s.rstrip('0').rstrip('.')
+        if display_s == '00':
+            return f'{h}:{m:02d}'
+        return f'{h}:{m:02d}:{display_s}'
+
+    def __float__(self):
+        return self.h + self.m / 60 + self.s / 3600
+
+    def __eq__(self, other):
+        return repr(self) == repr(other)
+
+    def __iter__(self):
+        yield self.h
+        yield self.m
+        yield self.s
+
+    def __add__(self, other):
+        if not isinstance(other, Hours):
+            return NotImplemented
+        return Hours(*(a + b for a, b in zip(self, other)))
+
+
+H = Hours

25-class-metaprog/hours/hours_test.py

@@ -0,0 +1,71 @@
+# content of test_expectation.py
+from math import isclose
+
+import pytest
+
+from hours import normalize, H
+
+HOURS_TO_HMS = [
+    [1, (1, 0, 0.0)],
+    [1.5, (1, 30, 0.0)],
+    [1.1, (1, 6, 0.0)],
+    [1.9, (1, 54, 0.0)],
+    [1.01, (1, 0, 36.0)],
+    [1.09, (1, 5, 24.0)],
+    [2 + 1/60, (2, 1, 0.0)],
+    [3 + 1/3600, (3, 0, 1.0)],
+    [1.251, (1, 15, 3.6)],
+]
+
+
+@pytest.mark.parametrize('hours, expected', HOURS_TO_HMS)
+def test_normalize(hours, expected):
+    h, m, s = expected
+    got_h, got_m, got_s = normalize(hours * 3600)
+    assert (h, m) == (got_h, got_m)
+    assert isclose(s, got_s, abs_tol=1e-12)
+    got_hours = got_h + got_m / 60 + got_s / 3600
+    assert isclose(hours, got_hours)
+
+
+@pytest.mark.parametrize('h, expected', [
+    (H[1], '1:00'),
+    (H[1:0], '1:00'),
+    (H[1:3], '1:03'),
+    (H[1:59], '1:59'),
+    (H[1:0:0], '1:00'),
+    (H[1:2:3], '1:02:03'),
+    (H[1:2:3.4], '1:02:03.4'),
+    (H[1:2:0.1], '1:02:00.1'),
+    (H[1:2:0.01], '1:02:00.01'),
+    (H[1:2:0.001], '1:02:00.001'),
+    (H[1:2:0.0001], '1:02'),
+])
+def test_repr(h, expected):
+    assert expected == repr(h), f'seconds: {h.s}'
+
+
+@pytest.mark.parametrize('expected, hms', HOURS_TO_HMS)
+def test_float(expected, hms):
+    got = float(H[slice(*hms)])
+    assert isclose(expected, got)
+
+
+@pytest.mark.parametrize('hms, units', [
+    ((0, 60, 0), 'minutes'),
+    ((0, 0, 60), 'seconds'),
+    ((0, 60, 60), 'minutes'),
+])
+def test_class_getitem_errors(hms, units):
+    with pytest.raises(ValueError) as excinfo:
+        H[slice(*hms)]
+    assert units in str(excinfo.value)
+
+
+@pytest.mark.parametrize('hms1, hms2, expected', [
+    (H[0:30], H[0:15], H[0:45]),
+    (H[0:30], H[0:30], H[1:00]),
+    (H[0:59:59], H[0:00:1], H[1:00]),
+])
+def test_add(hms1, hms2, expected):
+    assert expected == hms1 + hms2

25-class-metaprog/metabunch/README.md

@@ -0,0 +1,20 @@
+# Examples from Python in a Nutshell, 3rd edition
+
+The metaclass `MetaBunch` example in `original/bunch.py` is an exact copy of the
+last example in the _How a Metaclass Creates a Class_ section of 
+_Chapter 4: Object Oriented Python_ from  
+[_Python in a Nutshell, 3rd edition_](https://learning.oreilly.com/library/view/python-in-a/9781491913833)
+by Alex Martelli, Anna Ravenscroft, and Steve Holden.
+
+The version in `pre3.6/bunch.py` is slightly simplified by taking advantage
+of Python 3 `super()` and removing comments and docstrings,
+to make it easier to compare to the `from3.6` version.
+
+The version in `from3.6/bunch.py` is further simplified by taking advantage
+of the order-preserving `dict` that appeared in Python 3.6,
+as well as other simplifications,
+such as leveraging closures in `__init__` and `__repr__` 
+to avoid adding a `__defaults__` mapping to the class.
+
+The external behavior of all three versions is the same, and
+the test files `bunch_test.py` are identical in the three directories.

25-class-metaprog/metabunch/from3.6/bunch.py

@@ -0,0 +1,77 @@
+"""
+The `MetaBunch` metaclass is a simplified version of the
+last example in the _How a Metaclass Creates a Class_ section
+of _Chapter 4: Object Oriented Python_ from
+[_Python in a Nutshell, 3rd edition_](https://learning.oreilly.com/library/view/python-in-a/9781491913833)
+by Alex Martelli, Anna Ravenscroft, and Steve Holden.
+
+Here are a few tests. ``bunch_test.py`` has a few more.
+
+# tag::BUNCH_POINT_DEMO_1[]
+    >>> class Point(Bunch):
+    ...     x = 0.0
+    ...     y = 0.0
+    ...     color = 'gray'
+    ...
+    >>> Point(x=1.2, y=3, color='green')
+    Point(x=1.2, y=3, color='green')
+    >>> p = Point()
+    >>> p.x, p.y, p.color
+    (0.0, 0.0, 'gray')
+    >>> p
+    Point()
+
+# end::BUNCH_POINT_DEMO_1[]
+
+# tag::BUNCH_POINT_DEMO_2[]
+
+    >>> Point(x=1, y=2, z=3)
+    Traceback (most recent call last):
+      ...
+    AttributeError: 'Point' object has no attribute 'z'
+    >>> p = Point(x=21)
+    >>> p.y = 42
+    >>> p
+    Point(x=21, y=42)
+    >>> p.flavor = 'banana'
+    Traceback (most recent call last):
+      ...
+    AttributeError: 'Point' object has no attribute 'flavor'
+
+# end::BUNCH_POINT_DEMO_2[]
+"""
+
+# tag::METABUNCH[]
+class MetaBunch(type):  # <1>
+    def __new__(meta_cls, cls_name, bases, cls_dict):  # <2>
+
+        defaults = {}  # <3>
+
+        def __init__(self, **kwargs):  # <4>
+            for name, default in defaults.items():  # <5>
+                setattr(self, name, kwargs.pop(name, default))
+            if kwargs:  # <6>
+                setattr(self, *kwargs.popitem())
+
+        def __repr__(self):  # <7>
+            rep = ', '.join(f'{name}={value!r}'
+                            for name, default in defaults.items()
+                            if (value := getattr(self, name)) != default)
+            return f'{cls_name}({rep})'
+
+        new_dict = dict(__slots__=[], __init__=__init__, __repr__=__repr__)  # <8>
+
+        for name, value in cls_dict.items():  # <9>
+            if name.startswith('__') and name.endswith('__'):  # <10>
+                if name in new_dict:
+                    raise AttributeError(f"Can't set {name!r} in {cls_name!r}")
+                new_dict[name] = value
+            else:  # <11>
+                new_dict['__slots__'].append(name)
+                defaults[name] = value
+        return super().__new__(meta_cls, cls_name, bases, new_dict)  # <12>
+
+
+class Bunch(metaclass=MetaBunch):  # <13>
+    pass
+# end::METABUNCH[]

25-class-metaprog/metabunch/from3.6/bunch_test.py

@@ -0,0 +1,59 @@
+import pytest
+
+from bunch import Bunch
+
+class Point(Bunch):
+    """ A point has x and y coordinates, defaulting to 0.0,
+        and a color, defaulting to 'gray'—and nothing more,
+        except what Python and the metaclass conspire to add,
+        such as __init__ and __repr__
+    """
+    x = 0.0
+    y = 0.0
+    color = 'gray'
+
+
+def test_init_defaults():
+    p = Point()
+    assert repr(p) == 'Point()'
+
+
+def test_init():
+    p = Point(x=1.2, y=3.4, color='red')
+    assert repr(p) == "Point(x=1.2, y=3.4, color='red')"
+
+
+def test_init_wrong_argument():
+    with pytest.raises(AttributeError) as exc:
+        p = Point(x=1.2, y=3.4, flavor='coffee')
+    assert "no attribute 'flavor'" in str(exc.value)
+
+
+def test_slots():
+    p = Point()
+    with pytest.raises(AttributeError) as exc:
+        p.z = 5.6
+    assert "no attribute 'z'" in str(exc.value)
+
+
+def test_dunder_permitted():
+    class Cat(Bunch):
+        name = ''
+        weight = 0
+
+        def __str__(self):
+            return f'{self.name} ({self.weight} kg)'
+
+    cheshire = Cat(name='Cheshire')
+    assert str(cheshire) == 'Cheshire (0 kg)'
+
+
+def test_dunder_forbidden():
+    with pytest.raises(AttributeError) as exc:
+        class Cat(Bunch):
+            name = ''
+            weight = 0
+
+            def __init__(self):
+                pass
+    assert "Can't set '__init__' in 'Cat'" in str(exc.value)

25-class-metaprog/metabunch/nutshell3e/bunch.py

@@ -0,0 +1,85 @@
+import collections
+import warnings
+
+class MetaBunch(type):
+    """
+    Metaclass for new and improved "Bunch": implicitly defines
+    __slots__, __init__ and __repr__ from variables bound in
+    class scope.
+    A class statement for an instance of MetaBunch (i.e., for a
+    class whose metaclass is MetaBunch) must define only
+    class-scope data attributes (and possibly special methods, but
+    NOT __init__ and __repr__).  MetaBunch removes the data
+    attributes from class scope, snuggles them instead as items in
+    a class-scope dict named __dflts__, and puts in the class a
+    __slots__ with those attributes' names, an __init__ that takes
+    as optional named arguments each of them (using the values in
+    __dflts__ as defaults for missing ones), and a __repr__ that
+    shows the repr of each attribute that differs from its default
+    value (the output of __repr__ can be passed to __eval__ to make
+    an equal instance, as per usual convention in the matter, if
+    each non-default-valued attribute respects the convention too).
+
+    In v3, the order of data attributes remains the same as in the
+    class body; in v2, there is no such guarantee.
+    """
+    def __prepare__(name, *bases, **kwargs):
+        # precious in v3—harmless although useless in v2
+        return collections.OrderedDict()
+
+    def __new__(mcl, classname, bases, classdict):
+        """ Everything needs to be done in __new__, since
+            type.__new__ is where __slots__ are taken into account.
+        """
+        # define as local functions the __init__ and __repr__ that
+        # we'll use in the new class
+        def __init__(self, **kw):
+            """ Simplistic __init__: first set all attributes to
+                default values, then override those explicitly
+                passed in kw.
+            """
+            for k in self.__dflts__:
+                setattr(self, k, self.__dflts__[k])
+            for k in kw:
+                setattr(self, k, kw[k])
+        def __repr__(self):
+            """ Clever __repr__: show only attributes that differ
+                from default values, for compactness.
+            """
+            rep = ['{}={!r}'.format(k, getattr(self, k))
+                    for k in self.__dflts__
+                    if getattr(self, k) != self.__dflts__[k]
+                  ]
+            return '{}({})'.format(classname, ', '.join(rep))
+        # build the newdict that we'll use as class-dict for the
+        # new class
+        newdict = { '__slots__':[], 
+            '__dflts__':collections.OrderedDict(),
+            '__init__':__init__, '__repr__':__repr__, }
+        for k in classdict:
+            if k.startswith('__') and k.endswith('__'):
+                # dunder methods: copy to newdict, or warn
+                # about conflicts
+                if k in newdict:
+                    warnings.warn(
+                        "Can't set attr {!r} in bunch-class {!r}".
+                        format(k, classname))
+                else:
+                    newdict[k] = classdict[k]
+            else:
+                # class variables, store name in __slots__, and
+                # name and value as an item in __dflts__
+                newdict['__slots__'].append(k)
+                newdict['__dflts__'][k] = classdict[k]
+        # finally delegate the rest of the work to type.__new__
+        return super(MetaBunch, mcl).__new__(
+                     mcl, classname, bases, newdict)
+
+class Bunch(metaclass=MetaBunch):
+    """ For convenience: inheriting from Bunch can be used to get
+        the new metaclass (same as defining metaclass= yourself).
+
+        In v2, remove the (metaclass=MetaBunch) above and add
+        instead __metaclass__=MetaBunch as the class body.
+    """
+    pass

25-class-metaprog/metabunch/nutshell3e/bunch_test.py

@@ -0,0 +1,38 @@
+import pytest
+
+from bunch import Bunch
+
+class Point(Bunch):
+    """ A point has x and y coordinates, defaulting to 0.0, 
+        and a color, defaulting to 'gray'—and nothing more, 
+        except what Python and the metaclass conspire to add, 
+        such as __init__ and __repr__
+    """
+    x = 0.0
+    y = 0.0
+    color = 'gray'
+
+
+def test_init_defaults():
+    p = Point()
+    assert repr(p) == 'Point()'
+
+
+def test_init():
+    p = Point(x=1.2, y=3.4, color='red')
+    assert repr(p) == "Point(x=1.2, y=3.4, color='red')"
+
+
+def test_init_wrong_argument():
+    with pytest.raises(AttributeError) as exc:
+        p = Point(x=1.2, y=3.4, flavor='coffee')
+    assert "no attribute 'flavor'" in str(exc.value)
+
+
+def test_slots():
+    p = Point()
+    with pytest.raises(AttributeError) as exc:
+        p.z = 5.6
+    assert "no attribute 'z'" in str(exc.value)
+
+

25-class-metaprog/metabunch/original/bunch.py

@@ -0,0 +1,70 @@
+import warnings
+
+class metaMetaBunch(type):
+    """
+    metaclass for new and improved "Bunch": implicitly defines
+    __slots__, __init__ and __repr__ from variables bound in class scope.
+
+    An instance of metaMetaBunch (a class whose metaclass is metaMetaBunch)
+    defines only class-scope variables (and possibly special methods, but
+    NOT __init__ and __repr__!).  metaMetaBunch removes those variables from
+    class scope, snuggles them instead as items in a class-scope dict named
+    __dflts__, and puts in the class a __slots__ listing those variables'
+    names, an __init__ that takes as optional keyword arguments each of
+    them (using the values in __dflts__ as defaults for missing ones), and
+    a __repr__ that shows the repr of each attribute that differs from its
+    default value (the output of __repr__ can be passed to __eval__ to make
+    an equal instance, as per the usual convention in the matter).
+    """
+
+    def __new__(cls, classname, bases, classdict):
+        """ Everything needs to be done in __new__, since type.__new__ is
+            where __slots__ are taken into account.
+        """
+
+        # define as local functions the __init__ and __repr__ that we'll
+        # use in the new class
+
+        def __init__(self, **kw):
+            """ Simplistic __init__: first set all attributes to default
+                values, then override those explicitly passed in kw.
+            """
+            for k in self.__dflts__: setattr(self, k, self.__dflts__[k])
+            for k in kw: setattr(self, k, kw[k])
+
+        def __repr__(self):
+            """ Clever __repr__: show only attributes that differ from the
+                respective default values, for compactness.
+            """
+            rep = [ '%s=%r' % (k, getattr(self, k)) for k in self.__dflts__
+                    if getattr(self, k) != self.__dflts__[k]
+                  ]
+            return '%s(%s)' % (classname, ', '.join(rep))
+
+        # build the newdict that we'll use as class-dict for the new class
+        newdict = { '__slots__':[], '__dflts__':{},
+            '__init__':__init__, '__repr__':__repr__, }
+
+        for k in classdict:
+            if k.startswith('__'):
+                # special methods &c: copy to newdict, warn about conflicts
+                if k in newdict:
+                    warnings.warn("Can't set attr %r in bunch-class %r" % (
+                        k, classname))
+                else:
+                    newdict[k] = classdict[k]
+            else:
+                # class variables, store name in __slots__ and name and
+                # value as an item in __dflts__
+                newdict['__slots__'].append(k)
+                newdict['__dflts__'][k] = classdict[k]
+
+        # finally delegate the rest of the work to type.__new__
+        return type.__new__(cls, classname, bases, newdict)
+
+
+class MetaBunch(metaclass=metaMetaBunch):
+    """ For convenience: inheriting from MetaBunch can be used to get
+        the new metaclass (same as defining __metaclass__ yourself).
+    """
+    __metaclass__ = metaMetaBunch

25-class-metaprog/metabunch/original/bunch_test.py

@@ -0,0 +1,38 @@
+import pytest
+
+from bunch import MetaBunch
+
+class Point(MetaBunch):
+    """ A point has x and y coordinates, defaulting to 0.0,
+        and a color, defaulting to 'gray'—and nothing more,
+        except what Python and the metaclass conspire to add,
+        such as __init__ and __repr__
+    """
+    x = 0.0
+    y = 0.0
+    color = 'gray'
+
+
+def test_init_defaults():
+    p = Point()
+    assert repr(p) == 'Point()'
+
+
+def test_init():
+    p = Point(x=1.2, y=3.4, color='red')
+    assert repr(p) == "Point(x=1.2, y=3.4, color='red')"
+
+
+def test_init_wrong_argument():
+    with pytest.raises(AttributeError) as exc:
+        p = Point(x=1.2, y=3.4, flavor='coffee')
+    assert "no attribute 'flavor'" in str(exc.value)
+
+
+def test_slots():
+    p = Point()
+    with pytest.raises(AttributeError) as exc:
+        p.z = 5.6
+    assert "no attribute 'z'" in str(exc.value)
+
+

25-class-metaprog/metabunch/pre3.6/bunch.py

@@ -0,0 +1,41 @@
+import collections
+import warnings
+
+class MetaBunch(type):
+    def __prepare__(name, *bases, **kwargs):
+        return collections.OrderedDict()
+
+    def __new__(meta_cls, cls_name, bases, cls_dict):
+        def __init__(self, **kw):
+            for k in self.__defaults__:
+                setattr(self, k, self.__defaults__[k])
+            for k in kw:
+                setattr(self, k, kw[k])
+
+        def __repr__(self):
+            rep = ['{}={!r}'.format(k, getattr(self, k))
+                    for k in self.__defaults__
+                    if getattr(self, k) != self.__defaults__[k]
+                  ]
+            return '{}({})'.format(cls_name, ', '.join(rep))
+
+        new_dict = { '__slots__':[], 
+            '__defaults__':collections.OrderedDict(),
+            '__init__':__init__, '__repr__':__repr__, }
+
+        for k in cls_dict:
+            if k.startswith('__') and k.endswith('__'):
+                if k in new_dict:
+                    warnings.warn(
+                        "Can't set attr {!r} in bunch-class {!r}".
+                        format(k, cls_name))
+                else:
+                    new_dict[k] = cls_dict[k]
+            else:
+                new_dict['__slots__'].append(k)
+                new_dict['__defaults__'][k] = cls_dict[k]
+
+        return super().__new__(meta_cls, cls_name, bases, new_dict)
+
+class Bunch(metaclass=MetaBunch):
+    pass

25-class-metaprog/metabunch/pre3.6/bunch_test.py

@@ -0,0 +1,38 @@
+import pytest
+
+from bunch import Bunch
+
+class Point(Bunch):
+    """ A point has x and y coordinates, defaulting to 0.0, 
+        and a color, defaulting to 'gray'—and nothing more, 
+        except what Python and the metaclass conspire to add, 
+        such as __init__ and __repr__
+    """
+    x = 0.0
+    y = 0.0
+    color = 'gray'
+
+
+def test_init_defaults():
+    p = Point()
+    assert repr(p) == 'Point()'
+
+
+def test_init():
+    p = Point(x=1.2, y=3.4, color='red')
+    assert repr(p) == "Point(x=1.2, y=3.4, color='red')"
+
+
+def test_init_wrong_argument():
+    with pytest.raises(AttributeError) as exc:
+        p = Point(x=1.2, y=3.4, flavor='coffee')
+    assert "no attribute 'flavor'" in str(exc.value)
+
+
+def test_slots():
+    p = Point()
+    with pytest.raises(AttributeError) as exc:
+        p.z = 5.6
+    assert "no attribute 'z'" in str(exc.value)
+
+

25-class-metaprog/persistent/persistlib.py

@@ -4,16 +4,16 @@ A ``Persistent`` class definition::
     >>> class Movie(Persistent):
     ...     title: str
     ...     year: int
-    ...     megabucks: float
+    ...     box_office: float
 
 Implemented behavior::
 
     >>> Movie._connect()  # doctest: +ELLIPSIS
     <sqlite3.Connection object at 0x...>
-    >>> movie = Movie(title='The Godfather', year=1972, megabucks=137)
+    >>> movie = Movie(title='The Godfather', year=1972, box_office=137)
     >>> movie.title
     'The Godfather'
-    >>> movie.megabucks
+    >>> movie.box_office
     137.0
 
 Instances always have a ``._pk`` attribute, but it is ``None`` until the
@@ -32,7 +32,7 @@ using ``Movie[pk]``—item access on the class itself::
     >>> del movie
     >>> film = Movie[1]
     >>> film
-    Movie(title='The Godfather', year=1972, megabucks=137.0, _pk=1)
+    Movie(title='The Godfather', year=1972, box_office=137.0, _pk=1)
 
 By default, the table name is the class name lowercased, with an appended
 "s" for plural::
@@ -84,35 +84,12 @@ class Persistent:
             if not name.startswith('_')
         }
 
-    def __init_subclass__(cls, *, table: str = '', **kwargs: dict):
+    def __init_subclass__(cls, *, table: str = '', **kwargs: Any):
         super().__init_subclass__(**kwargs)  # type:ignore
         cls._TABLE_NAME = table if table else cls.__name__.lower() + 's'
         for name, py_type in cls._fields().items():
             setattr(cls, name, Field(name, py_type))
 
-    @staticmethod
-    def _connect(db_path: str = db.DEFAULT_DB_PATH):
-        return db.connect(db_path)
-
-    @classmethod
-    def _ensure_table(cls) -> str:
-        if not cls._TABLE_READY:
-            db.ensure_table(cls._TABLE_NAME, cls._fields())
-            cls._TABLE_READY = True
-        return cls._TABLE_NAME
-
-    def __class_getitem__(cls, pk: int) -> 'Persistent':
-        field_names = ['_pk'] + list(cls._fields())
-        values = db.fetch_record(cls._TABLE_NAME, pk)
-        return cls(**dict(zip(field_names, values)))
-
-    def _asdict(self) -> dict[str, Any]:
-        return {
-            name: getattr(self, name)
-            for name, attr in self.__class__.__dict__.items()
-            if isinstance(attr, Field)
-        }
-
     def __init__(self, *, _pk=None, **kwargs):
         field_names = self._asdict().keys()
         for name, arg in kwargs.items():
@@ -131,6 +108,32 @@ class Persistent:
             return f'{cls_name}({kwargs})'
         return f'{cls_name}({kwargs}, _pk={self._pk})'
 
+    def _asdict(self) -> dict[str, Any]:
+        return {
+            name: getattr(self, name)
+            for name, attr in self.__class__.__dict__.items()
+            if isinstance(attr, Field)
+        }
+
+
+    # database methods
+
+    @staticmethod
+    def _connect(db_path: str = db.DEFAULT_DB_PATH):
+        return db.connect(db_path)
+
+    @classmethod
+    def _ensure_table(cls) -> str:
+        if not cls._TABLE_READY:
+            db.ensure_table(cls._TABLE_NAME, cls._fields())
+            cls._TABLE_READY = True
+        return cls._TABLE_NAME
+
+    def __class_getitem__(cls, pk: int) -> 'Persistent':
+        field_names = ['_pk'] + list(cls._fields())
+        values = db.fetch_record(cls._TABLE_NAME, pk)
+        return cls(**dict(zip(field_names, values)))
+
     def _save(self) -> int:
         table = self.__class__._ensure_table()
         if self._pk is None:

25-class-metaprog/qualname/fakedjango.py

@@ -0,0 +1,5 @@
+class models:
+    class Model:
+        "nothing to see here"
+    class IntegerField:
+        "nothing to see here"

25-class-metaprog/qualname/models.py

@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+ 
+from fakedjango import models
+
+class Ox(models.Model):
+    horn_length = models.IntegerField()
+
+    class Meta:
+        ordering = ['horn_length']
+        verbose_name_plural = 'oxen'
+
+print(Ox.Meta.__name__)
+print(Ox.Meta.__qualname__)