Factorial of a large number in python

Question

Here\'s my approach to factorials:

def factorial(n):
    \'\'\'Returns factorial of n\'\'\'
    r = 1
    for i in range(1, n + 1):
        r *= i
    return         


        

Answer 1

You can use the reduce function rather than explicit looping thus:

>>> from functools import reduce
>>> mul = int.__mul__
>>> len(str(reduce(mul, range(2,100001), 1)))
456574
>>> 

In Python 2 you need to use longs: long.__mul__, and len(str(reduce(mul, range(2L,100001L), 1L)))