instance_method_as_a_function.py

In [1]: class ListA(object):
   ...:     def __init__(self, x, y):
   ...:         self.x = x
   ...:         self.y = y
   ...:     def sum(self):
   ...:         return self.x + self.y
   ...:

In [2]: a = ListA(4, 5)

In [3]: a
Out[3]: <__main__.ListA at 0x101cd0310>

In [4]: a.sum
Out[4]: <bound method ListA.sum of <__main__.ListA object at 0x101cd0310>>

In [5]: a.sum()
Out[5]: 9

In [6]: b = ListA(3,4)

In [7]: b.sum()
Out[7]: 7

In [8]: map(ListA.sum, [a, b])
Out[8]: [9, 7]