Is there a math nCr function in python? [duplicate]

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

import operator as opfrom functools import reducedef 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

Do you want iteration? itertools.combinations. Common usage:

>>> import itertools>>> itertools.combinations('abcd',2)<itertools.combinations object at 0x01348F30>>>> list(itertools.combinations('abcd',2))[('a', 'b'), ('a', 'c'), ('a', 'd'), ('b', 'c'), ('b', 'd'), ('c', 'd')]>>> [''.join(x) for x in itertools.combinations('abcd',2)]['ab', 'ac', 'ad', 'bc', 'bd', 'cd']

If you just need to compute the formula, use math.factorial:

import mathdef nCr(n,r):    f = math.factorial    return f(n) / f(r) / f(n-r)if __name__ == '__main__':    print nCr(4,2)

In Python 3, use the integer division // instead of / to avoid overflows:

return f(n) // f(r) // f(n-r)

Output

6