001 阶乘

    1. #return the factorial of a given number#
    2. #返回阶乘#
    4. def FirstFactorial(num): 
    6.   factorial = 1
    8.   for i in range(1, num+1):
    9.     # multiply each number between 1 and num  
    10.     # factorial = 1 * 1 = 1
    11.     # factorial = 1 * 2 = 2
    12.     # factorial = 2 * 3 = 6
    13.     # factorial = 6 * 4 = 24
    14.     # ...
    15.     factorial = factorial * i
    17.   return factorial
    19. print FirstFactorial(4)