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factorial() in Python

  • Difficulty Level : Easy
  • Last Updated : 11 Oct, 2017

Not many people know, but python offers a direct function that can compute the factorial of a number without writing the whole code for computing factorial.

Naive method to compute factorial




# Python code to demonstrate naive method
# to compute factorial
n = 23
fact = 1
  
for i in range(1,n+1):
    fact = fact * i
      
print ("The factorial of 23 is : ",end="")
print (fact)

Output :

The factorial of 23 is : 25852016738884976640000

Using math.factorial()

This method is defined in “math” module of python. Because it has C type internal implementation, it is fast.



math.factorial(x)
Parameters :
x : The number whose factorial has to be computed.
Return value :
Returns the factorial of desired number.
Exceptions : 
Raises Value error if number is negative or non-integral.




# Python code to demonstrate math.factorial()
import math
  
print ("The factorial of 23 is : ", end="")
print (math.factorial(23))

Output :

The factorial of 23 is : 25852016738884976640000

Exceptions in math.factorial()

  • If give number is Negative :




    # Python code to demonstrate math.factorial()
    # Exceptions ( negative number )
      
    import math
      
    print ("The factorial of -5 is : ",end="")
      
    # raises exception
    print (math.factorial(-5))

    Output :

    The factorial of -5 is : 
    

    Runtime Error :

    Traceback (most recent call last):
      File "/home/f29a45b132fac802d76b5817dfaeb137.py", line 9, in 
        print (math.factorial(-5))
    ValueError: factorial() not defined for negative values
    
  • If given number is Non – Integral Value :




    # Python code to demonstrate math.factorial()
    # Exceptions ( Non-Integral number )
      
    import math
      
    print ("The factorial of 5.6 is : ",end="")
      
    # raises exception
    print (math.factorial(5.6))

    Output :

    The factorial of 5.6 is : 
    

    Runtime Error :

    Traceback (most recent call last):
      File "/home/3987966b8ca9cbde2904ad47dfdec124.py", line 9, in 
        print (math.factorial(5.6))
    ValueError: factorial() only accepts integral values
    

This article is contributed by Manjeet Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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