'Demonstrate effective use of super()'
import collections
import logging
logging.basicConfig(level='INFO')
class LoggingDict(dict):
# Simple example of extending a builtin class
def __setitem__(self, key, value):
logging.info('Setting %r to %r' % (key, value))
return super().__setitem__(key, value)
class LoggingOD(LoggingDict, collections.OrderedDict):
# Build new functionality by reordering the MRO
pass
ld = LoggingDict([('red', 1), ('green', 2), ('blue', 3)])
print(ld)
ld['red'] = 10
ld = LoggingOD([('red', 1), ('green', 2), ('blue', 3)])
print(ld)
ld['red'] = 10
print('-' * 20)
# ------- Show the order that the methods are called -------
def show_call_order(cls, methname):
'Utility to show the call chain'
classes = [cls for cls in cls.__mro__ if methname in cls.__dict__]
print(' ==> '.join('%s.%s' % (cls.__name__, methname) for cls in classes))
show_call_order(LoggingOD, '__setitem__')
show_call_order(LoggingOD, '__iter__')
# ------- Getting the argument signatures to match ----------
class Shape:
def __init__(self, *, shapename, **kwds):
self.shapename = shapename
super().__init__(**kwds)
class ColoredShape(Shape):
def __init__(self, *, color, **kwds):
self.color = color
super().__init__(**kwds)
cs = ColoredShape(color='red', shapename='circle')
# -------- Making sure a root exists --------------------------
class Root:
def draw(self):
pass # the delegation chain stops here
class Shape(Root):
def __init__(self, *, shapename, **kwds):
self.shapename = shapename
super().__init__(**kwds)
def draw(self):
print('Drawing. Setting shape to:', self.shapename)
super().draw()
class ColoredShape(Shape):
def __init__(self, *, color, **kwds):
self.color = color
super().__init__(**kwds)
def draw(self):
print('Drawing. Setting color to:', self.color)
super().draw()
ColoredShape(color='blue', shapename='square').draw()
# ------- Show how to wrap a non-cooperative class --------
class Moveable:
# non-cooperative class that doesn't use super()
def __init__(self, x, y):
self.x = x
self.y = y
def draw(self):
print('Drawing at position:', self.x, self.y)
class MoveableWrapper(Root):
# make a cooperative wrapper class for Moveable
def __init__(self, *, x, y, **kwds):
self.moveable = Moveable(x, y)
super().__init__(**kwds)
def draw(self):
self.moveable.draw()
super().draw()
class MovableColoredShape(ColoredShape, MoveableWrapper):
pass
MovableColoredShape(color='red', shapename='triangle', x=10, y=20).draw()
# -------- Complete example ---------------------------------
from collections import Counter, OrderedDict
class OrderedCounter(Counter, OrderedDict):
'Counter that remembers the order elements are first encountered'
def __repr__(self):
return '%s(%r)' % (self.__class__.__name__, OrderedDict(self))
def __reduce__(self):
return self.__class__, (OrderedDict(self),)
oc = OrderedCounter('abracadabra')
print(oc)
Diff to Previous Revision
--- revision 2 2011-05-31 06:01:49
+++ revision 3 2011-05-31 06:17:53
@@ -95,7 +95,7 @@
class MovableColoredShape(ColoredShape, MoveableWrapper):
pass
-MovableColoredShape(color='blue', shapename='square', x=10, y=20).draw()
+MovableColoredShape(color='red', shapename='triangle', x=10, y=20).draw()
# -------- Complete example ---------------------------------
