update from Atlas with major reorg

attic/metaprog/plainpoint.py

@@ -0,0 +1,25 @@
+"""
+A class equivalent to the class statement below would be generated by this code:
+
+    >>> import collections
+    >>> Point = collections.plainclass('Point', 'x y')
+"""
+
+class Point(object):
+    __slots__ = ['x', 'y']  # save memory in the likely event there are many instances
+
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+    def __repr__(self):
+        return 'Point({!r}, {!r})'.format(self.x, self.y)
+
+    def __eq__(self, other):
+        if not isinstance(other, Point):
+            return NotImplemented
+        return self.x == other.x and self.y == other.y
+
+    def __iter__(self, other):  # support unpacking
+        yield self.x
+        yield self.y

attic/metaprog/prop_inheritance.py

@@ -0,0 +1,29 @@
+"""
+Alex Martelli, _Python in a Nutshell, 2e._ (O'Reilly, 2006), p. 101
+
+==========================
+Properties and inheritance
+==========================
+
+Properties are inherited normally, just like any other attribute.
+However, there’s a little trap for the unwary: the methods called
+upon to access a property are those that are defined in the class
+in which the property itself is defined, without intrinsic use of
+further overriding that may happen in subclasses. For example:
+"""
+
+class B(object):
+
+    def f(self):
+        return 23
+
+    g = property(f)
+
+class C(B):
+
+    def f(self):
+        return 42
+
+c = C()
+
+print(c.g) # prints 23, not 42

attic/metaprog/special_attrs.py

@@ -0,0 +1,44 @@
+
+'''
+4.13. Special Attributes
+
+The implementation adds a few special read-only attributes to
+several object types, where they are relevant.
+
+Some of these are not reported by the dir() built-in function.
+
+https://docs.python.org/3/library/stdtypes.html#special-attributes
+'''
+
+
+obj_attrs = {'__dict__', '__class__'}
+
+cls_data_attrs = {'__slots__', '__bases__', '__name__', '__qualname__', '__mro__'}
+
+cls_methods = {'mro', '__subclasses__'}
+
+cls_attrs = cls_data_attrs | cls_methods
+
+
+an_object = object()
+
+class EmptyClass():
+    pass
+
+an_instance = EmptyClass()
+
+class EmptySlots():
+    __slots__ = ()
+
+a_slots_instance = EmptySlots()
+
+
+objs = EmptyClass, EmptySlots, an_object, an_instance, a_slots_instance
+
+for obj in objs:
+    print('-' * 60)
+    print(repr(obj), ':', type(obj))
+    dir_obj = set(dir(obj))
+    print('obj_attrs not listed:', sorted(obj_attrs - dir_obj))
+    print('all cls_attrs       :', sorted(cls_attrs))
+    print('cls_attrs not listed:', sorted(cls_attrs - dir_obj))

attic/metaprog/spreadsheet.py

@@ -0,0 +1,44 @@
+"""
+Spreadsheet example adapted from Raymond Hettinger's `recipe`__
+
+__ http://code.activestate.com/recipes/355045-spreadsheet/
+
+Demonstration::
+
+    >>> from math import sin, pi
+    >>> ss = Spreadsheet(sin=sin, pi=pi)
+    >>> ss['a1'] = '-5'
+    >>> ss['a2'] = 'a1*6'
+    >>> ss['a3'] = 'a2*7'
+    >>> ss['a3']
+    -210
+    >>> ss['b1'] = 'sin(pi/4)'
+    >>> ss['b1']  # doctest:+ELLIPSIS
+    0.707106781186...
+    >>> ss.getformula('b1')
+    'sin(pi/4)'
+    >>> ss['c1'] = 'abs(a2)'
+    >>> ss['c1']
+    30
+    >>> ss['d1'] = '3*'
+    >>> ss['d1']
+    Traceback (most recent call last):
+      ...
+    SyntaxError: unexpected EOF while parsing
+"""
+
+
+class Spreadsheet:
+
+    def __init__(self, **tools):
+        self._cells = {}
+        self._tools = tools
+
+    def __setitem__(self, key, formula):
+        self._cells[key] = formula
+
+    def getformula(self, key):
+        return self._cells[key]
+
+    def __getitem__(self, key):
+        return eval(self._cells[key], self._tools, self)

attic/metaprog/spreadsheet2.py

@@ -0,0 +1,54 @@
+"""
+Spreadsheet example adapted from Raymond Hettinger's `recipe`__
+
+__ http://code.activestate.com/recipes/355045-spreadsheet/
+
+Demonstration::
+
+    >>> from math import sin, pi
+    >>> ss = Spreadsheet(sin=sin, pi=pi, abs=abs)
+    >>> ss['a1'] = '-5'
+    >>> ss['a2'] = 'a1*6'
+    >>> ss['a3'] = 'a2*7'
+    >>> ss['a3']
+    -210
+    >>> ss['b1'] = 'sin(pi/4)'
+    >>> ss['b1']  # doctest:+ELLIPSIS
+    0.707106781186...
+    >>> ss.getformula('b1')
+    'sin(pi/4)'
+    >>> ss['c1'] = 'abs(a2)'
+    >>> ss['c1']
+    30
+    >>> ss['c2'] = 'len(a2)'
+    >>> ss['c2']
+    Traceback (most recent call last):
+      ...
+    NameError: name 'len' is not defined
+    >>> ss['d1'] = '3*'
+    Traceback (most recent call last):
+      ...
+    SyntaxError: unexpected EOF while parsing ['d1'] = '3*'
+"""
+
+
+class Spreadsheet:
+
+    def __init__(self, **tools):
+        self._cells = {}
+        self._tools = {'__builtins__' : {}}
+        self._tools.update(tools)
+
+    def __setitem__(self, key, formula):
+        try:
+            compile(formula, '<__setitem__>', 'eval')
+        except SyntaxError as exc:
+            msg = '{} [{!r}] = {!r}'.format(exc.msg, key, formula)
+            raise SyntaxError(msg)
+        self._cells[key] = formula
+
+    def getformula(self, key):
+        return self._cells[key]
+
+    def __getitem__(self, key):
+        return eval(self._cells[key], self._tools, self)