gistfile1.py

>>> class foo(object):
...     def bla(self):
...             print 1
... 
>>> a = foo()
>>> a.bla
<bound method foo.bla of <__main__.foo object at 0xb750dfac>>
>>> del foo.bla
>>> a.bla
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'foo' object has no attribute 'bla'
>>> a.bla()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'foo' object has no attribute 'bla'