On Sat, Jul 2, 2011 at 2:59 PM, Saqib Ali <saqib.ali...@gmail.com> wrote: <snip> > Then I instantiate 2 instances of myClass2 (c & d). I then change the > value of c.mySet. Bizarrely changing the value of c.mySet also affects > the value of d.mySet which I haven't touched at all!?!?! Can someone > explain this very strange behavior to me? I can't understand it for > the life of me. <snip> > class myClass2: > > mySet = sets.Set(range(1,10)) > > def clearSet(self): > self.mySet.clear() > > def __str__(self): > return str(len(self.mySet))
Please read a tutorial on object-oriented programming in Python. The official one is pretty good: http://docs.python.org/tutorial/classes.html If you do, you'll find out that your class (as written) has mySet as a class (Java lingo: static) variable, *not* an instance variable; thus, it is shared by all instances of the class, and hence the behavior you observed. Instance variables are properly created in the __init__() initializer method, *not* directly in the class body. Your class would be correctly rewritten as: class MyClass2(object): def __init__(self): self.mySet = sets.Set(range(1,10)) def clearSet(self): # ...rest same as before... Cheers, Chris -- http://rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
