renumbering chapters >= 19

22-dyn-attr-prop/README.rst

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+Sample code for Chapter 19 - "Dynamic attributes and properties"
+
+From the book "Fluent Python" by Luciano Ramalho (O'Reilly, 2015)
+http://shop.oreilly.com/product/0636920032519.do

22-dyn-attr-prop/blackknight.py

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+"""
+This class is inspired by the Black Knight scene in the movie
+"Monty Python and the Holy Grail", where King Arthur fights the
+Black Knight, slicing off his arms and legs, but the knight
+refuses to concede defeat.
+
+# tag::BLACK_KNIGHT_DEMO[]
+    >>> knight = BlackKnight()
+    >>> knight.member
+    next member is:
+    'an arm'
+    >>> del knight.member
+    BLACK KNIGHT (loses an arm) -- 'Tis but a scratch.
+    >>> del knight.member
+    BLACK KNIGHT (loses another arm) -- It's just a flesh wound.
+    >>> del knight.member
+    BLACK KNIGHT (loses a leg) -- I'm invincible!
+    >>> del knight.member
+    BLACK KNIGHT (loses another leg) -- All right, we'll call it a draw.
+
+# end::BLACK_KNIGHT_DEMO[]
+"""
+
+# tag::BLACK_KNIGHT[]
+class BlackKnight:
+
+    def __init__(self):
+        self.phrases = [
+            ('an arm', "'Tis but a scratch."),
+            ('another arm', "It's just a flesh wound."),
+            ('a leg', "I'm invincible!"),
+            ('another leg', "All right, we'll call it a draw.")
+        ]
+
+    @property
+    def member(self):
+        print('next member is:')
+        return self.phrases[0][0]
+
+    @member.deleter
+    def member(self):
+        member, text = self.phrases.pop(0)
+        print(f'BLACK KNIGHT (loses {member}) -- {text}')
+# end::BLACK_KNIGHT[]

22-dyn-attr-prop/bulkfood/bulkfood_v1.py

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+"""
+A line item for a bulk food order has description, weight and price fields.
+A ``subtotal`` method gives the total price for that line item::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> raisins.weight, raisins.description, raisins.price
+    (10, 'Golden raisins', 6.95)
+    >>> raisins.subtotal()
+    69.5
+
+But, without validation, these public attributes can cause trouble::
+
+# tag::LINEITEM_PROBLEM_V1[]
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> raisins.subtotal()
+    69.5
+    >>> raisins.weight = -20  # garbage in...
+    >>> raisins.subtotal()    # garbage out...
+    -139.0
+
+# end::LINEITEM_PROBLEM_V1[]
+
+"""
+
+
+# tag::LINEITEM_V1[]
+class LineItem:
+
+    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_V1[]

22-dyn-attr-prop/bulkfood/bulkfood_v2.py

@@ -0,0 +1,63 @@
+"""
+
+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 check is also performed on instantiation::
+
+    >>> walnuts = LineItem('walnuts', 0, 10.00)
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+The proteced attribute can still be accessed if needed for some reason, such as
+white box testing)::
+
+    >>> raisins._LineItem__weight
+    10
+
+"""
+
+
+# tag::LINEITEM_V2[]
+class LineItem:
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight  # <1>
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price
+
+    @property  # <2>
+    def weight(self):  # <3>
+        return self.__weight  # <4>
+
+    @weight.setter  # <5>
+    def weight(self, value):
+        if value > 0:
+            self.__weight = value  # <6>
+        else:
+            raise ValueError('value must be > 0')  # <7>
+# end::LINEITEM_V2[]

22-dyn-attr-prop/bulkfood/bulkfood_v2b.py

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+"""
+
+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 check is also performed on instantiation::
+
+    >>> walnuts = LineItem('walnuts', 0, 10.00)
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+The proteced attribute can still be accessed if needed for some reason, such as
+white box testing)::
+
+    >>> raisins._LineItem__weight
+    10
+
+"""
+
+
+# tag::LINEITEM_V2B[]
+class LineItem:
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price
+
+    def get_weight(self):  # <1>
+        return self.__weight
+
+    def set_weight(self, value):  # <2>
+        if value > 0:
+            self.__weight = value
+        else:
+            raise ValueError('value must be > 0')
+
+    weight = property(get_weight, set_weight)  # <3>
+
+# end::LINEITEM_V2B[]

22-dyn-attr-prop/bulkfood/bulkfood_v2prop.py

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+"""
+
+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 properties are stored in
+instance attributes, created in each ``LineItem`` instance::
+
+# tag::LINEITEM_V2_PROP_DEMO[]
+    >>> nutmeg = LineItem('Moluccan nutmeg', 8, 13.95)
+    >>> nutmeg.weight, nutmeg.price  # <1>
+    (8, 13.95)
+    >>> sorted(vars(nutmeg).items())  # <2>
+    [('description', 'Moluccan nutmeg'), ('price', 13.95), ('weight', 8)]
+
+# end::LINEITEM_V2_PROP_DEMO[]
+
+"""
+
+
+# tag::LINEITEM_V2_PROP_FACTORY_FUNCTION[]
+def quantity(storage_name):  # <1>
+
+    def qty_getter(instance):  # <2>
+        return instance.__dict__[storage_name]  # <3>
+
+    def qty_setter(instance, value):  # <4>
+        if value > 0:
+            instance.__dict__[storage_name] = value  # <5>
+        else:
+            raise ValueError('value must be > 0')
+
+    return property(qty_getter, qty_setter)  # <6>
+# end::LINEITEM_V2_PROP_FACTORY_FUNCTION[]
+
+
+# tag::LINEITEM_V2_PROP_CLASS[]
+class LineItem:
+    weight = quantity('weight')  # <1>
+    price = quantity('price')  # <2>
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight  # <3>
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price  # <4>
+# end::LINEITEM_V2_PROP_CLASS[]

22-dyn-attr-prop/doc_property.py

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+"""
+Example of property documentation
+
+    >>> f = Foo()
+    >>> f.bar = 77
+    >>> f.bar
+    77
+    >>> Foo.bar.__doc__
+    'The bar attribute'
+"""
+
+# tag::DOC_PROPERTY[]
+class Foo:
+
+    @property
+    def bar(self):
+        '''The bar attribute'''
+        return self.__dict__['bar']
+
+    @bar.setter
+    def bar(self, value):
+        self.__dict__['bar'] = value
+# end::DOC_PROPERTY[]

22-dyn-attr-prop/oscon/demo_schedule2.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+
+import shelve
+
+from schedule_v2 import DB_NAME, CONFERENCE, load_db
+from schedule_v2 import DbRecord, Event
+
+with shelve.open(DB_NAME) as db:
+    if CONFERENCE not in db:
+        load_db(db)
+
+    DbRecord.set_db(db)
+    event = DbRecord.fetch('event.33950')
+    print(event)
+    print(event.venue)
+    print(event.venue.name)
+    for spkr in event.speakers:
+        print(f'{spkr.serial}:', spkr.name)
+
+    print(repr(Event.venue))
+
+    event2 = DbRecord.fetch('event.33451')
+    print(event2)
+    print(event2.fetch)
+    print(event2.venue)

22-dyn-attr-prop/oscon/explore0.py

@@ -0,0 +1,65 @@
+"""
+explore0.py: Script to explore the OSCON schedule feed
+
+# tag::EXPLORE0_DEMO[]
+    >>> import json
+    >>> raw_feed = json.load(open('data/osconfeed.json'))
+    >>> feed = FrozenJSON(raw_feed)  # <1>
+    >>> len(feed.Schedule.speakers)  # <2>
+    357
+    >>> feed.keys()
+    dict_keys(['Schedule'])
+    >>> sorted(feed.Schedule.keys())  # <3>
+    ['conferences', 'events', 'speakers', 'venues']
+    >>> for key, value in sorted(feed.Schedule.items()): # <4>
+    ...     print(f'{len(value):3} {key}')
+    ...
+      1 conferences
+    484 events
+    357 speakers
+     53 venues
+    >>> feed.Schedule.speakers[-1].name  # <5>
+    'Carina C. Zona'
+    >>> talk = feed.Schedule.events[40]
+    >>> type(talk)  # <6>
+    <class 'explore0.FrozenJSON'>
+    >>> talk.name
+    'There *Will* Be Bugs'
+    >>> talk.speakers  # <7>
+    [3471, 5199]
+    >>> talk.flavor  # <8>
+    Traceback (most recent call last):
+      ...
+    KeyError: 'flavor'
+
+# end::EXPLORE0_DEMO[]
+
+"""
+
+# tag::EXPLORE0[]
+from collections import abc
+
+
+class FrozenJSON:
+    """A read-only façade for navigating a JSON-like object
+       using attribute notation
+    """
+
+    def __init__(self, mapping):
+        self.__data = dict(mapping)  # <1>
+
+    def __getattr__(self, name):  # <2>
+        try:
+            return getattr(self.__data, name)  # <3>
+        except AttributeError:
+            return FrozenJSON.build(self.__data[name])  # <4>
+
+    @classmethod
+    def build(cls, obj):  # <5>
+        if isinstance(obj, abc.Mapping):  # <6>
+            return cls(obj)
+        elif isinstance(obj, abc.MutableSequence):  # <7>
+            return [cls.build(item) for item in obj]
+        else:  # <8>
+            return obj
+# end::EXPLORE0[]

22-dyn-attr-prop/oscon/explore1.py

@@ -0,0 +1,78 @@
+"""
+explore1.py: Script to explore the OSCON schedule feed
+
+    >>> import json
+    >>> raw_feed = json.load(open('data/osconfeed.json'))
+    >>> feed = FrozenJSON(raw_feed)
+    >>> len(feed.Schedule.speakers)
+    357
+    >>> sorted(feed.Schedule.keys())
+    ['conferences', 'events', 'speakers', 'venues']
+    >>> for key, value in sorted(feed.Schedule.items()):
+    ...     print(f'{len(value):3} {key}')
+    ...
+      1 conferences
+    484 events
+    357 speakers
+     53 venues
+    >>> feed.Schedule.speakers[-1].name
+    'Carina C. Zona'
+    >>> talk = feed.Schedule.events[40]
+    >>> type(talk)
+    <class 'explore1.FrozenJSON'>
+    >>> talk.name
+    'There *Will* Be Bugs'
+    >>> talk.speakers
+    [3471, 5199]
+    >>> talk.flavor
+    Traceback (most recent call last):
+      ...
+    KeyError: 'flavor'
+
+Handle keywords by appending a `_`.
+
+# tag::EXPLORE1_DEMO[]
+
+    >>> grad = FrozenJSON({'name': 'Jim Bo', 'class': 1982})
+    >>> grad.name
+    'Jim Bo'
+    >>> grad.class_
+    1982
+
+# end::EXPLORE1_DEMO[]
+
+"""
+
+from collections import abc
+import keyword
+
+
+class FrozenJSON:
+    """A read-only façade for navigating a JSON-like object
+       using attribute notation
+    """
+
+# tag::EXPLORE1[]
+    def __init__(self, mapping):
+        self.__data = {}
+        for key, value in mapping.items():
+            if keyword.iskeyword(key):  # <1>
+                key += '_'
+            self.__data[key] = value
+# end::EXPLORE1[]
+
+    def __getattr__(self, name):
+        if hasattr(self.__data, name):
+            return getattr(self.__data, name)
+        else:
+            return FrozenJSON.build(self.__data[name])
+
+    @classmethod
+    def build(cls, obj):
+        if isinstance(obj, abc.Mapping):
+            return cls(obj)
+        elif isinstance(obj, abc.MutableSequence):
+            return [cls.build(item) for item in obj]
+        else:  # <8>
+            return obj
+

22-dyn-attr-prop/oscon/explore2.py

@@ -0,0 +1,54 @@
+"""
+explore2.py: Script to explore the OSCON schedule feed
+
+    >>> import json
+    >>> raw_feed = json.load(open('data/osconfeed.json'))
+    >>> feed = FrozenJSON(raw_feed)
+    >>> len(feed.Schedule.speakers)
+    357
+    >>> sorted(feed.Schedule.keys())
+    ['conferences', 'events', 'speakers', 'venues']
+    >>> feed.Schedule.speakers[-1].name
+    'Carina C. Zona'
+    >>> talk = feed.Schedule.events[40]
+    >>> talk.name
+    'There *Will* Be Bugs'
+    >>> talk.speakers
+    [3471, 5199]
+    >>> talk.flavor
+    Traceback (most recent call last):
+      ...
+    KeyError: 'flavor'
+
+"""
+
+# tag::EXPLORE2[]
+from collections import abc
+import keyword
+
+class FrozenJSON:
+    """A read-only façade for navigating a JSON-like object
+       using attribute notation
+    """
+
+    def __new__(cls, arg):  # <1>
+        if isinstance(arg, abc.Mapping):
+            return super().__new__(cls)  # <2>
+        elif isinstance(arg, abc.MutableSequence):  # <3>
+            return [cls(item) for item in arg]
+        else:
+            return arg
+
+    def __init__(self, mapping):
+        self.__data = {}
+        for key, value in mapping.items():
+            if keyword.iskeyword(key):
+                key += '_'
+            self.__data[key] = value
+
+    def __getattr__(self, name):
+        if hasattr(self.__data, name):
+            return getattr(self.__data, name)
+        else:
+            return FrozenJSON(self.__data[name])  # <4>
+# end::EXPLORE2[]

22-dyn-attr-prop/oscon/osconfeed-sample.json

@@ -0,0 +1,32 @@
+{ "Schedule": 
+  { "conferences": [{"serial": 115 }],
+    "events": [
+      { "serial": 34505,
+        "name": "Why Schools Don´t Use Open Source to Teach Programming",
+        "event_type": "40-minute conference session",
+        "time_start": "2014-07-23 11:30:00",
+        "time_stop": "2014-07-23 12:10:00",
+        "venue_serial": 1462,
+        "description": "Aside from the fact that high school programming...",
+        "website_url": "http://oscon.com/oscon2014/public/schedule/detail/34505", 
+        "speakers": [157509],
+        "categories": ["Education"] }
+    ],
+    "speakers": [
+      { "serial": 157509,
+        "name": "Robert Lefkowitz",
+        "photo": null,
+        "url": "http://sharewave.com/",
+        "position": "CTO",
+        "affiliation": "Sharewave",
+        "twitter": "sharewaveteam",
+        "bio": "Robert ´r0ml´ Lefkowitz is the CTO at Sharewave, a startup..." }
+    ],
+    "venues": [
+      { "serial": 1462,
+        "name": "F151",
+        "category": "Conference Venues" }
+    ]
+  }
+}
+    

22-dyn-attr-prop/oscon/osconfeed_explore.rst

@@ -0,0 +1,20 @@
+>>> import json
+>>> with open('data/osconfeed.json') as fp:
+...     feed = json.load(fp)  # <1>
+>>> sorted(feed['Schedule'].keys())  # <2>
+['conferences', 'events', 'speakers', 'venues']
+>>> for key, value in sorted(feed['Schedule'].items()):
+...     print(f'{len(value):3} {key}')  # <3>
+...
+  1 conferences
+484 events
+357 speakers
+ 53 venues
+>>> feed['Schedule']['speakers'][-1]['name']  # <4>
+'Carina C. Zona'
+>>> feed['Schedule']['speakers'][-1]['serial']  # <5>
+141590
+>>> feed['Schedule']['events'][40]['name']
+'There *Will* Be Bugs'
+>>> feed['Schedule']['events'][40]['speakers']  # <6>
+[3471, 5199]

22-dyn-attr-prop/oscon/runtests.sh

@@ -0,0 +1,2 @@
+#!/bin/bash
+pytest --doctest-modules $2 $1 test_$1

22-dyn-attr-prop/oscon/schedule_v1.py

@@ -0,0 +1,39 @@
+"""
+schedule_v1.py: traversing OSCON schedule data
+
+# tag::SCHEDULE1_DEMO[]
+    >>> records = load(JSON_PATH)  # <1>
+    >>> speaker = records['speaker.3471']  # <2>
+    >>> speaker  # <3>
+    <Record serial=3471>
+    >>> speaker.name, speaker.twitter  # <4>
+    ('Anna Martelli Ravenscroft', 'annaraven')
+
+# end::SCHEDULE1_DEMO[]
+
+"""
+
+# tag::SCHEDULE1[]
+import json
+
+JSON_PATH = 'data/osconfeed.json'
+
+class Record:
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)  # <1>
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        return f'<{cls_name} serial={self.serial!r}>'  # <2>
+
+def load(path=JSON_PATH):
+    records = {}  # <3>
+    with open(path) as fp:
+        raw_data = json.load(fp)  # <4>
+    for collection, raw_records in raw_data['Schedule'].items():  # <5>
+        record_type = collection[:-1]  # <6>
+        for raw_record in raw_records:
+            key = f'{record_type}.{raw_record["serial"]}' # <7>
+            records[key] = Record(**raw_record)  # <8>
+    return records
+# end::SCHEDULE1[]

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

@@ -0,0 +1,76 @@
+"""
+schedule_v2.py: property to get venue linked to an event
+
+# tag::SCHEDULE2_DEMO[]
+    >>> event = Record.fetch('event.33950')  # <1>
+    >>> event  # <2>
+    <Event 'There *Will* Be Bugs'>
+    >>> event.venue  # <3>
+    <Record serial=1449>
+    >>> event.venue.name  # <4>
+    'Portland 251'
+    >>> event.venue_serial  # <5>
+    1449
+
+# end::SCHEDULE2_DEMO[]
+"""
+
+# tag::SCHEDULE2_RECORD[]
+import inspect  # <1>
+import json
+
+JSON_PATH = 'data/osconfeed.json'
+
+class Record:
+
+    __index = None  # <2>
+
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        return f'<{cls_name} serial={self.serial!r}>'
+
+    @staticmethod  # <3>
+    def fetch(key):
+        if Record.__index is None:  # <4>
+            Record.__index = load()
+        return Record.__index[key]  # <5>
+# end::SCHEDULE2_RECORD[]
+
+
+# tag::SCHEDULE2_EVENT[]
+class Event(Record):  # <1>
+
+    def __repr__(self):
+        if hasattr(self, 'name'):  # <2>
+            cls_name = self.__class__.__name__
+            return f'<{cls_name} {self.name!r}>'
+        else:
+            return super().__repr__()
+
+    @property
+    def venue(self):
+        key = f'venue.{self.venue_serial}'
+        return self.__class__.fetch(key)  # <3>
+# end::SCHEDULE2_EVENT[]
+
+# tag::SCHEDULE2_LOAD[]
+def load(path=JSON_PATH):
+    records = {}
+    with open(path) as fp:
+        raw_data = json.load(fp)
+    for collection, raw_records in raw_data['Schedule'].items():
+        record_type = collection[:-1]  # <1>
+        cls_name = record_type.capitalize()  # <2>
+        cls = globals().get(cls_name, Record)  # <3>
+        if inspect.isclass(cls) and issubclass(cls, Record):  # <4>
+            factory = cls  # <5>
+        else:
+            factory = Record  # <6>
+        for raw_record in raw_records:  # <7>
+            key = f'{record_type}.{raw_record["serial"]}'
+            records[key] = factory(**raw_record)  # <8>
+    return records
+# end::SCHEDULE2_LOAD[]

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

@@ -0,0 +1,86 @@
+"""
+schedule_v3.py: property to get list of event speakers
+
+    >>> event = Record.fetch('event.33950')
+    >>> event
+    <Event 'There *Will* Be Bugs'>
+    >>> event.venue
+    <Record serial=1449>
+    >>> event.venue_serial
+    1449
+    >>> event.venue.name
+    'Portland 251'
+
+# tag::SCHEDULE3_DEMO[]
+    >>> for spkr in event.speakers:
+    ...     print(f'{spkr.serial}: {spkr.name}')
+    3471: Anna Martelli Ravenscroft
+    5199: Alex Martelli
+
+# end::SCHEDULE3_DEMO[]
+"""
+
+import inspect
+import json
+
+JSON_PATH = 'data/osconfeed.json'
+
+class Record:
+
+    __index = None
+
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        return f'<{cls_name} serial={self.serial!r}>'
+
+    @staticmethod
+    def fetch(key):
+        if Record.__index is None:
+            Record.__index = load()
+        return Record.__index[key]
+
+
+class Event(Record):
+
+    def __repr__(self):
+        if hasattr(self, 'name'):  # <3>
+            cls_name = self.__class__.__name__
+            return f'<{cls_name} {self.name!r}>'
+        else:
+            return super().__repr__()  # <4>
+
+    @property
+    def venue(self):
+        key = f'venue.{self.venue_serial}'
+        return self.__class__.fetch(key)
+
+# tag::SCHEDULE3_SPEAKERS[]
+    @property
+    def speakers(self):
+        spkr_serials = self.__dict__['speakers']  # <1>
+        fetch = self.__class__.fetch
+        return [fetch(f'speaker.{key}')
+                for key in spkr_serials]  # <2>
+
+# end::SCHEDULE3_SPEAKERS[]
+
+
+def load(path=JSON_PATH):
+    records = {}
+    with open(path) as fp:
+        raw_data = json.load(fp)
+    for collection, raw_records in raw_data['Schedule'].items():
+        record_type = collection[:-1]
+        cls_name = record_type.capitalize()
+        cls = globals().get(cls_name, Record)
+        if inspect.isclass(cls) and issubclass(cls, Record):
+            factory = cls
+        else:
+            factory = Record
+        for raw_record in raw_records:
+            key = f'{record_type}.{raw_record["serial"]}'
+            records[key] = factory(**raw_record)
+    return records

22-dyn-attr-prop/oscon/schedule_v4.py

@@ -0,0 +1,94 @@
+"""
+schedule_v4.py: homegrown cached property for speakers
+
+    >>> event = Record.fetch('event.33950')
+
+# tag::SCHEDULE4_DEMO[]
+    >>> event  # <1>
+    <Event 'There *Will* Be Bugs'>
+    >>> event.venue  # <2>
+    <Record serial=1449>
+    >>> event.venue.name  # <3>
+    'Portland 251'
+    >>> for spkr in event.speakers:  # <4>
+    ...     print(f'{spkr.serial}: {spkr.name}')
+    ...
+    3471: Anna Martelli Ravenscroft
+    5199: Alex Martelli
+
+# end::SCHEDULE4_DEMO[]
+"""
+
+import json
+import inspect
+
+JSON_PATH = 'data/osconfeed.json'
+
+class Record:
+
+    __index = None
+
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        return f'<{cls_name} serial={self.serial!r}>'
+
+    @staticmethod
+    def fetch(key):
+        if Record.__index is None:
+            Record.__index = load()
+        return Record.__index[key]
+
+
+# tag::SCHEDULE4_INIT[]
+class Event(Record):
+
+    def __init__(self, **kwargs):
+        self.__speaker_objs = None
+        super().__init__(**kwargs)
+
+# end::SCHEDULE4_INIT[]
+
+    def __repr__(self):
+        if hasattr(self, 'name'):
+            cls_name = self.__class__.__name__
+            return f'<{cls_name} {self.name!r}>'
+        else:
+            return super().__repr__()  # <4>
+
+    @property
+    def venue(self):
+        key = f'venue.{self.venue_serial}'
+        return self.__class__.fetch(key)
+
+# tag::SCHEDULE4_CACHE[]
+    @property
+    def speakers(self):
+        if self.__speaker_objs is None:
+            spkr_serials = self.__dict__['speakers']
+            fetch = self.__class__.fetch
+            self.__speaker_objs = [fetch(f'speaker.{key}')
+                    for key in spkr_serials]
+        return self.__speaker_objs
+
+# end::SCHEDULE4_CACHE[]
+
+
+def load(path=JSON_PATH):
+    records = {}
+    with open(path) as fp:
+        raw_data = json.load(fp)
+    for collection, raw_records in raw_data['Schedule'].items():
+        record_type = collection[:-1]
+        cls_name = record_type.capitalize()
+        cls = globals().get(cls_name, Record)
+        if inspect.isclass(cls) and issubclass(cls, Record):
+            factory = cls
+        else:
+            factory = Record
+        for raw_record in raw_records:
+            key = f'{record_type}.{raw_record["serial"]}'
+            records[key] = factory(**raw_record)
+    return records

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

@@ -0,0 +1,86 @@
+"""
+schedule_v4.py: homegrown cached property for speakers
+
+    >>> event = Record.fetch('event.33950')
+
+# tag::SCHEDULE4_DEMO[]
+    >>> event  # <1>
+    <Event 'There *Will* Be Bugs'>
+    >>> event.venue  # <2>
+    <Record serial=1449>
+    >>> event.venue.name  # <3>
+    'Portland 251'
+    >>> for spkr in event.speakers:  # <4>
+    ...     print(f'{spkr.serial}: {spkr.name}')
+    3471: Anna Martelli Ravenscroft
+    5199: Alex Martelli
+
+# end::SCHEDULE4_DEMO[]
+"""
+
+import inspect
+import json
+
+JSON_PATH = 'data/osconfeed.json'
+
+class Record:
+
+    __index = None
+
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        return f'<{cls_name} serial={self.serial!r}>'
+
+    @staticmethod
+    def fetch(key):
+        if Record.__index is None:
+            Record.__index = load()
+        return Record.__index[key]
+
+
+class Event(Record):
+
+    def __repr__(self):
+        if hasattr(self, 'name'):
+            cls_name = self.__class__.__name__
+            return f'<{cls_name} {self.name!r}>'
+        else:
+            return super().__repr__()  # <4>
+
+    @property
+    def venue(self):
+        key = f'venue.{self.venue_serial}'
+        return self.__class__.fetch(key)
+
+# tag::SCHEDULE4_HASATTR_CACHE[]
+    @property
+    def speakers(self):
+        if not hasattr(self, '__speaker_objs'):  # <1>
+            spkr_serials = self.__dict__['speakers']
+            fetch = self.__class__.fetch
+            self.__speaker_objs = [fetch(f'speaker.{key}')
+                    for key in spkr_serials]
+        return self.__speaker_objs  # <2>
+
+# end::SCHEDULE4_HASATTR_CACHE[]
+
+
+def load(path=JSON_PATH):
+    records = {}
+    with open(path) as fp:
+        raw_data = json.load(fp)
+    for collection, raw_records in raw_data['Schedule'].items():
+        record_type = collection[:-1]
+        cls_name = record_type.capitalize()
+        cls = globals().get(cls_name, Record)
+        if inspect.isclass(cls) and issubclass(cls, Record):
+            factory = cls
+        else:
+            factory = Record
+        for raw_record in raw_records:
+            key = f'{record_type}.{raw_record["serial"]}'
+            records[key] = factory(**raw_record)
+    return records

22-dyn-attr-prop/oscon/schedule_v5.py

@@ -0,0 +1,89 @@
+"""
+schedule_v5.py: cached properties using functools
+
+    >>> event = Record.fetch('event.33950')
+    >>> event
+    <Event 'There *Will* Be Bugs'>
+    >>> event.venue
+    <Record serial=1449>
+    >>> event.venue_serial
+    1449
+    >>> event.venue.name
+    'Portland 251'
+
+# tag::SCHEDULE3_DEMO[]
+    >>> for spkr in event.speakers:  # <3>
+    ...     print(f'{spkr.serial}: {spkr.name}')
+    ...
+    3471: Anna Martelli Ravenscroft
+    5199: Alex Martelli
+
+# end::SCHEDULE3_DEMO[]
+"""
+
+import json
+import inspect
+
+from functools import cached_property, cache
+
+JSON_PATH = 'data/osconfeed.json'
+
+class Record:
+
+    __index = None
+
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        return f'<{cls_name} serial={self.serial!r}>'
+
+    @staticmethod
+    def fetch(key):
+        if Record.__index is None:
+            Record.__index = load()
+        return Record.__index[key]
+
+
+class Event(Record):
+
+    def __repr__(self):
+        if hasattr(self, 'name'):
+            cls_name = self.__class__.__name__
+            return f'<{cls_name} {self.name!r}>'
+        else:
+            return super().__repr__()
+
+# tag::SCHEDULE5_CACHED_PROPERTY[]
+    @cached_property
+    def venue(self):
+        key = f'venue.{self.venue_serial}'
+        return self.__class__.fetch(key)
+# end::SCHEDULE5_CACHED_PROPERTY[]
+# tag::SCHEDULE5_PROPERTY_OVER_CACHE[]
+    @property  # <1>
+    @cache  # <2>
+    def speakers(self):
+        spkr_serials = self.__dict__['speakers']
+        fetch = self.__class__.fetch
+        return [fetch(f'speaker.{key}')
+                for key in spkr_serials]
+# end::SCHEDULE5_PROPERTY_OVER_CACHE[]
+
+def load(path=JSON_PATH):
+    records = {}
+    with open(path) as fp:
+        raw_data = json.load(fp)
+    for collection, raw_records in raw_data['Schedule'].items():
+        record_type = collection[:-1]
+        cls_name = record_type.capitalize()
+        cls = globals().get(cls_name, Record)
+        if inspect.isclass(cls) and issubclass(cls, Record):
+            factory = cls
+        else:
+            factory = Record
+        for raw_record in raw_records:
+            key = f'{record_type}.{raw_record["serial"]}'
+            records[key] = factory(**raw_record)
+    return records

22-dyn-attr-prop/oscon/test_schedule_v1.py

@@ -0,0 +1,24 @@
+import pytest
+
+import schedule_v1 as schedule
+
+
+@pytest.yield_fixture
+def records():
+    yield schedule.load(schedule.JSON_PATH)
+
+
+def test_load(records):
+    assert len(records) == 895
+
+
+def test_record_attr_access():
+    rec = schedule.Record(spam=99, eggs=12)
+    assert rec.spam == 99
+    assert rec.eggs == 12
+
+
+def test_venue_record(records):
+    venue = records['venue.1469']
+    assert venue.serial == 1469
+    assert venue.name == 'Exhibit Hall C'

22-dyn-attr-prop/oscon/test_schedule_v2.py

@@ -0,0 +1,48 @@
+import pytest
+
+import schedule_v2 as schedule
+
+@pytest.yield_fixture
+def records():
+    yield schedule.load(schedule.JSON_PATH)
+
+
+def test_load(records):
+    assert len(records) == 895
+
+
+def test_record_attr_access():
+    rec = schedule.Record(spam=99, eggs=12)
+    assert rec.spam == 99
+    assert rec.eggs == 12
+
+
+def test_venue_record(records):
+    venue = records['venue.1469']
+    assert venue.serial == 1469
+    assert venue.name == 'Exhibit Hall C'
+
+
+def test_fetch_speaker_record():
+    speaker = schedule.Record.fetch('speaker.3471')
+    assert speaker.name == 'Anna Martelli Ravenscroft'
+
+
+def test_event_type():
+    event = schedule.Record.fetch('event.33950')
+    assert type(event) is schedule.Event
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+
+
+def test_event_repr():
+    event = schedule.Record.fetch('event.33950')
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+    event2 = schedule.Event(serial=77, kind='show')
+    assert repr(event2) == '<Event serial=77>'
+
+
+def test_event_venue():
+    event = schedule.Record.fetch('event.33950')
+    assert event.venue_serial == 1449
+    assert event.venue == schedule.Record.fetch('venue.1449')
+    assert event.venue.name == 'Portland 251'

22-dyn-attr-prop/oscon/test_schedule_v3.py

@@ -0,0 +1,59 @@
+import pytest
+
+import schedule_v3 as schedule
+
+@pytest.yield_fixture
+def records():
+    yield schedule.load(schedule.JSON_PATH)
+
+
+def test_load(records):
+    assert len(records) == 895
+
+
+def test_record_attr_access():
+    rec = schedule.Record(spam=99, eggs=12)
+    assert rec.spam == 99
+    assert rec.eggs == 12
+
+
+def test_venue_record(records):
+    venue = records['venue.1469']
+    assert venue.serial == 1469
+    assert venue.name == 'Exhibit Hall C'
+
+
+def test_fetch_speaker_record():
+    speaker = schedule.Record.fetch('speaker.3471')
+    assert speaker.name == 'Anna Martelli Ravenscroft'
+
+
+def test_event_type():
+    event = schedule.Record.fetch('event.33950')
+    assert type(event) is schedule.Event
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+
+
+def test_event_repr():
+    event = schedule.Record.fetch('event.33950')
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+    event2 = schedule.Event(serial=77, kind='show')
+    assert repr(event2) == '<Event serial=77>'
+
+
+def test_event_venue():
+    event = schedule.Record.fetch('event.33950')
+    assert event.venue_serial == 1449
+    assert event.venue == schedule.Record.fetch('venue.1449')
+    assert event.venue.name == 'Portland 251'
+
+
+def test_event_speakers():
+    event = schedule.Record.fetch('event.33950')
+    assert len(event.speakers) == 2
+    anna, alex = [schedule.Record.fetch(f'speaker.{s}') for s in (3471, 5199)]
+    assert event.speakers == [anna, alex]
+
+def test_event_no_speakers():
+    event = schedule.Record.fetch('event.36848')
+    assert event.speakers == []

22-dyn-attr-prop/oscon/test_schedule_v4.py

@@ -0,0 +1,59 @@
+import pytest
+
+import schedule_v4 as schedule
+
+@pytest.yield_fixture
+def records():
+    yield schedule.load(schedule.JSON_PATH)
+
+
+def test_load(records):
+    assert len(records) == 895
+
+
+def test_record_attr_access():
+    rec = schedule.Record(spam=99, eggs=12)
+    assert rec.spam == 99
+    assert rec.eggs == 12
+
+
+def test_venue_record(records):
+    venue = records['venue.1469']
+    assert venue.serial == 1469
+    assert venue.name == 'Exhibit Hall C'
+
+
+def test_fetch_speaker_record():
+    speaker = schedule.Record.fetch('speaker.3471')
+    assert speaker.name == 'Anna Martelli Ravenscroft'
+
+
+def test_event_type():
+    event = schedule.Record.fetch('event.33950')
+    assert type(event) is schedule.Event
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+
+
+def test_event_repr():
+    event = schedule.Record.fetch('event.33950')
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+    event2 = schedule.Event(serial=77, kind='show')
+    assert repr(event2) == '<Event serial=77>'
+
+
+def test_event_venue():
+    event = schedule.Record.fetch('event.33950')
+    assert event.venue_serial == 1449
+    assert event.venue == schedule.Record.fetch('venue.1449')
+    assert event.venue.name == 'Portland 251'
+
+
+def test_event_speakers():
+    event = schedule.Record.fetch('event.33950')
+    assert len(event.speakers) == 2
+    anna, alex = [schedule.Record.fetch(f'speaker.{s}') for s in (3471, 5199)]
+    assert event.speakers == [anna, alex]
+
+def test_event_no_speakers():
+    event = schedule.Record.fetch('event.36848')
+    assert event.speakers == []

22-dyn-attr-prop/oscon/test_schedule_v5.py

@@ -0,0 +1,59 @@
+import pytest
+
+import schedule_v5 as schedule
+
+@pytest.yield_fixture
+def records():
+    yield schedule.load(schedule.JSON_PATH)
+
+
+def test_load(records):
+    assert len(records) == 895
+
+
+def test_record_attr_access():
+    rec = schedule.Record(spam=99, eggs=12)
+    assert rec.spam == 99
+    assert rec.eggs == 12
+
+
+def test_venue_record(records):
+    venue = records['venue.1469']
+    assert venue.serial == 1469
+    assert venue.name == 'Exhibit Hall C'
+
+
+def test_fetch_speaker_record():
+    speaker = schedule.Record.fetch('speaker.3471')
+    assert speaker.name == 'Anna Martelli Ravenscroft'
+
+
+def test_event_type():
+    event = schedule.Record.fetch('event.33950')
+    assert type(event) is schedule.Event
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+
+
+def test_event_repr():
+    event = schedule.Record.fetch('event.33950')
+    assert repr(event) == "<Event 'There *Will* Be Bugs'>"
+    event2 = schedule.Event(serial=77, kind='show')
+    assert repr(event2) == '<Event serial=77>'
+
+
+def test_event_venue():
+    event = schedule.Record.fetch('event.33950')
+    assert event.venue_serial == 1449
+    assert event.venue == schedule.Record.fetch('venue.1449')
+    assert event.venue.name == 'Portland 251'
+
+
+def test_event_speakers():
+    event = schedule.Record.fetch('event.33950')
+    assert len(event.speakers) == 2
+    anna, alex = [schedule.Record.fetch(f'speaker.{s}') for s in (3471, 5199)]
+    assert event.speakers == [anna, alex]
+
+def test_event_no_speakers():
+    event = schedule.Record.fetch('event.36848')
+    assert event.speakers == []

22-dyn-attr-prop/pseudo_construction.py

@@ -0,0 +1,10 @@
+# pseudo-code for object construction
+def make(the_class, some_arg):
+    new_object = the_class.__new__(some_arg)
+    if isinstance(new_object, the_class):
+        the_class.__init__(new_object, some_arg)
+    return new_object
+
+# the following statements are roughly equivalent
+x = Foo('bar')
+x = make(Foo, 'bar')