import cmath def nCr(n, r): """Return the number of ways to choose r elements of a set of n.""" return cmath.exp( cmath.lfactorial(n) - cmath.lfactorial(r) - cmath.lfactorial(n-r) ) if __name__ == "__main__": import sys if len(sys.argv) != 3: sys.stderr.write("USAGE: %s n r\nPrints n-choose-r.\n" % sys.argv[0]) sys.exit(1) n, r = map(float, sys.argv[1:]) print nCr(n, r)