>>> class obj:
...     def __init__(self):
...         self.counter = 0
...     def inc(self):
...         self.counter += 1
...

>>> a = obj()
>>> from copy import copy
>>> b = copy(a)
>>> a.inc()
>>> b.inc()
>>> b.inc()
>>> b.inc()
>>> print a.counter, b.counter
1 3