python factorial

factorial.py

#!/usr/bin/env python
#-*- coding:utf-8 -*-

"""
by hx, 2015.11.24
version:python2.7.x
"""

def factorial(x):
    res = 1
    for i in xrange(2, x+1):
        res *= i
    return res

def fact_1(x):
    return x>1 and x*fact_1(x-1) or 1

def fact_2(x):
    f = lambda x: x>1 and x*f(x-1) or 1
    return f(x)


#@tailcall  #NameError: name 'tailcall' is not defined
def fact_3(x, acc=1):
    if x:
        return fact_3(x.__sub__(1), acc.__mul__(x))
    else:
        return acc
def fact_4(x):
    import math
    return math.factorial(x)

if __name__ == "__main__":
    import sys

    print(factorial(6))

    print(fact_1(6))
    print(fact_2(6))
    print(fact_3(6))
    print(fact_4(6))