Itertools permutations method explained

Itertools permutations returns successive r length permutations of elements in the iterable. If r is not specified or is None, then r defaults to the length of the iterable and all possible full-length permutations are generated.

from itertools import permutations

#how many possible permutations of 2 letters are there?
perms = list(permutations('abcd',2))
print perms
print len(perms)

[('a', 'b'), ('a', 'c'), ('a', 'd'), ('b', 'a'), ('b', 'c'), ('b', 'd'), ('c', '
a'), ('c', 'b'), ('c', 'd'), ('d', 'a'), ('d', 'b'), ('d', 'c')]
12