Python Program to Find Factorial of a Number
Factorial of a Number can be calculated in many ways. Some of them are by using a for loop, or using a recursion function or a while loop.
In the following Python Factorial Examples, we will find factorial of a given whole number, using the above said procedures.
Problem Statement – Factorial of a Number
Factorial of a number n is given by,
n! = n*(n-1)*(n-2)*...3*2*1
Run this program
0! = 1 1! = 1 2! = 2*1 = 2 3! = 3*2*1 = 6 4! = 4*3*2*1 = 24
You have to read n from user through console input. And print the answer to the console.
Example 1: Factorial using For Loop and Range
In the following example, we shall use Python For Loop to find Factorial. For a range(1,n+1) of given n, multiply the element over each iteration and return the result after coming out of the loop.
def factorial(n): result = 1 for i in range(1,n+1): result = result*i return result n = int(input('Enter a number: ')) result = factorial(n) print(n,'! = ',result,sep="")
We have not validated if the number is negative. You may write the validation to check if the number is not negative and then proceed with finding the factorial.
C:\python>python factorial.py Enter a number: 4 4! = 24 C:\python>python factorial.py Enter a number: 6 6! = 720 C:\python>python factorial.py Enter a number: 12 12! = 479001600
Example 2: Factorial using Recursive Function
Recursive functions are popular among budding programmers. But when it comes to performance, recursion is not a preferable choice in Python.
#recursion function def factorial(n): return 1 if (n==1 or n==0) else n * factorial(n - 1); #read input from user n = int(input('Enter a number: ')) #call recursion function result = factorial(n) #print result print(result)
Example 3: Factorial using While Loop
We shall use Python While Loop in this solution of finding factorial of a number.
#function computes factorial of a given number def factorial(n): result = 1 i=1 while i<=n: result*=i i+=1 return result #read input from user n = int(input('Enter a number: ')) #calculate factorial result = factorial(n) print(result)
In this tutorial of Python Examples, we learned different ways to write a Python Program to compute factorial of a given number.