Python Magic Methods – Documentation for Special Methods (__init__, __new__, __len__)

This example uses memoization, basically storing values in a table (dictionary in this case) so you can look them up later instead of recalculating them.

Here we use a simple class with a __call__ method to calculate factorials (through a callable object) instead of a factorial function that contains a static variable (as that's not possible in Python).

class Factorial:
    def __init__(self):
        self.cache = {}
    def __call__(self, n):
        if n not in self.cache:
            if n == 0:
                self.cache[n] = 1
            else:
                self.cache[n] = n * self.__call__(n-1)
        return self.cache[n]

fact = Factorial()

Now you have a fact object which is callable, just like every other function. For example

for i in xrange(10):                                                             
    print("{}! = {}".format(i, fact(i)))

# output
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880

And it is also stateful.

Check this out.

https://docs.python.org/3/howto/descriptor.html#class-methods

You can also take a look at the source code for class and static method objects, in funcobject.c:

http://hg.python.org/cpython/file/69b416cd1727/Objects/funcobject.c

Class method object definition starts on line 694, while static method object definition starts on line 852. (I do find it kind of funny that they have items titled "method" in funcobject.c when methodobject.c also exists.)