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How do I create static class data and static class methods?
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(Continued from previous question...)
How do I create static class data and static class methods?
Static data (in the sense of C++ or Java) is easy; static methods (again in the sense of C++ or Java) are not supported directly.
For static data, simply define a class attribute. To assign a new value to the attribute, you have to explicitly use the class name in the assignment:
class C:
count = 0 # number of times C.__init__ called
def __init__(self):
C.count = C.count + 1
def getcount(self):
return C.count # or return self.count
c.count also refers to C.count for any c such that isinstance(c, C) holds, unless overridden by c itself or by some class on the base-class search path from c.__class__ back to C.
Caution: within a method of C, an assignment like self.count = 42 creates a new and unrelated instance vrbl named "count" in self's own dict. Rebinding of a class-static data name must always specify the class whether inside a method or not:
C.count = 314
Static methods are possible when you're using new-style classes:
class C:
def static(arg1, arg2, arg3):
# No 'self' parameter!
...
static = staticmethod(static)
However, a far more straightforward way to get the effect of a static method is via a simple module-level function:
def getcount():
return C.count
If your code is structured so as to define one class (or tightly related class hierarchy) per module, this supplies the desired encapsulation.
(Continued on next question...)
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