puzzlement about classmethod

[Faheem Mitha]

Hi,

Consider the following small script.

My understanding of how this works is that, conceptually, class B
holds a separate copy of variable x from class A.

Nearly everything behaves the way I would expect, except that setting
x to 12 in A using class_setx at the beginning also sets the value for
x in B. However, the converse (setting x in B using class_setx), does
not change the value in A, which I would consider to be the expected
behavior.

However, after that the two x variables appear to behave
independently. Can anyone explain to me why this is so?

                                               Regards, Faheem Mitha.

******************************************************************
#!/usr/bin/python

class A(object):
    x = 0
    def class_getx(cls):
        return cls.x
    class_getx = classmethod(class_getx)
    def class_setx(cls, _x):
        cls.x = _x
    class_setx = classmethod(class_setx)
    def getx(self):
        return type(self).x
    def setx(self, _x):
        type(self).x = _x

class B(A):
    pass

def printx():
    print "*** begin printing values of x... ***"
    print "Fetching from A using class_getx gives %s"%(A.class_getx())
    print "Fetching from B using class_getx gives %s"%(B.class_getx())
    print "Fetching from A using instance a and getx gives %s"%(a.getx())
    print "Fetching from B using instance b and getx gives %s"%(b.getx())
    print "*** end printing values of x... ***"

a = A()
b = B()
printx()
print "setting x to 12 in A using class_setx"; A.class_setx(12)
printx()
print "setting x to 15 in B using class_setx"; B.class_setx(15)
printx()
print "setting x to 10 in A using class_setx"
A.class_setx(10)
printx()
print "setting x to 44 in A using instance a and setx"; a.setx(55)
printx()
print "setting x to 22 in B using instance b and setx"; b.setx(22)
printx()