Python : computing number of ways to choose K items from N items

Question

What is the Pythonic way to compute the number of ways to choose k items from n items without repetition and with order?

Answer 1

You can use the perm() function of Python module 'math'.

math.perm(n, k=None)

• Return the number of ways to choose k items from n items without repetition and with order.
• Evaluates to n! / (n - k)! when k <= n and evaluates to zero when k > n.
• If k is not specified or is None, then k defaults to n and the function returns n!.

E.g.

>>> import math
>>> math.perm(7,3)
210
>>> math.perm(3,1)
3
>>> math.perm(3,4)
0
>>> math.perm(5,3)
60