gistfile1.txt

>>> class Foo(object):
...     def bar(self, blah):
...         print self, blah
...
>>> Foo.bar
<unbound method Foo.bar>
>>> Foo.bar(None, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unbound method bar() must be called with Foo instance as first argument (got NoneType instance instead)
>>> Foo.bar(Foo(), 2)
<__main__.Foo object at 0x1f7d2d0> 2