Don't do this

classmethod.py

class Foo(object):
    @classmethod
    def bar(cls,x):
        cls.x = x
    def p(self):
        print self.x

a = Foo()
a.bar(1)
a.p()               # 1

b = Foo()
b.bar(2)
b.p()               # 2

a.p()               # 2, not what we wanted