Is there a math nCr function in python?

Question

Possible Duplicates:
Statistics: combinations in Python
counting combinations and permutations efficiently
Project euler problem in python (problem 53)

I'm looking to see if built in with the math library in python is the nCr (n Choose r) function:

I understand that this can be programmed but I thought that I'd check to see if it's already built in before I do.

Answer 1

The following program calculates nCr in an efficient manner (compared to calculating factorials etc.)

import operator as op
from functools import reduce

def ncr(n, r):
    r = min(r, n-r)
    numer = reduce(op.mul, range(n, n-r, -1), 1)
    denom = reduce(op.mul, range(1, r+1), 1)
    return numer // denom  # or / in Python 2

---

As of Python 3.8, binomial coefficients are available in the standard library as math.comb:

>>> from math import comb
>>> comb(10,3)
120