Using Reduce Function in Python To Find Factorial

Question

Hi I'm trying to write a function to find the factorial product of any given number. For example for factorial (6) I would get the product of 6*5*3*2*1.

so for factorial(3) the output would be 6.

The functions I have so far are:

import functools 

def mult(x, y):
    return x * y


def factorial(n):
    if n == 0:
        return 1
    else:
        functools.reduce(mult(n,factorial(n - 1)))

But I keep getting an error that Python is expecting 2 arguments and 1 is given. I know I have to use range somehow but I can't figure it out. How do I edit my existing code so that it runs properly?

Answer 1

you can do this pretty easily:

>>> import functools, operator
>>> functools.reduce(operator.mul, xrange(1, 6))
120

Note that the first argument is a function (you're passing the result of a function call). the second argument is an iterable. Also note that written this way, no recursion is needed...

^{operator.mul is equivalent to your mult function}

Answer 2

import functools

def factorial(n):
    if n == 0:
        return 1
    else:
        return functools.reduce(lambda x,y: x*y, range(1,n+1))

print factorial(3)

Of course you can use you own multi function instead of the lambda if you prefer.