Alan G wrote:
> So If I have a heirarchy of shapes and want a class method that
> only operates on the shape class itself, not on all the
> subclasses then I have to use staticmethod whereas if I want
> the class method to act on shape and each of its sub classes
> I must use a classmethod. The canonical example being counting
> instances. staticmethod would only allow me to count shapes
> but class method would allow me to count all the sub classes
> separately.
Sounds good so far.
Mind you this would require reprogramming the
> class method for each new shape which is probably a bad
> idea - overriding would be a better approach IMHO...
Not sure why you think you have to write a new classmethod for each shape.
Suppose you want to maintain creation counts for each class. Here is one way to
do it using classmethods:
class Shape(object):
_count = 0 # Default for classes with no instances (cls.count() never
called)
@classmethod
def count(cls):
try:
cls._count += 1
except AttributeError:
cls._count = 1
@classmethod
def showCount(cls):
print 'Class %s has count = %s' % (cls.__name__, cls._count)
def __init__(self):
self.count()
class Point(Shape): pass
class Line(Shape): pass
p, p2, p = Point(), Point(), Point()
Point.showCount()
Line.showCount()
l = Line()
Line.showCount()
### prints
Class Point has count = 3
Class Line has count = 0
Class Line has count = 1
Kent
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