In this post, We will be going to see different ways to write a code in Python for the factorial of a number.

Formula for finding factorial of a Number N : N * (N – 1) * (N – 2) * (N – 3) * ……* 2 * 1.

Note:

 N must be a Non-Negative Integers.

Example:

Input: Number = 6
Output: Factorial of 6 is 720. (6! = 6*5*4*3*2*1)
                                               
Input: Number = 5
Output:  Factorial of 5 is 120. (5! = 5*4*3*2*1)

Now, Let’s see the Codes:

Code 1: Using math library.
In this, we are importing the whole math library into this program then use the factorial() method.

# import math library 
# inside this program
import math

# given input
number = 5

# call factorial() method of 
# math library and then print
# the result
print("Factorial of", number, 
      ":", math.factorial(number))

Output:

Factorial of 5 : 120

Code 2: Using math library.
In this, we are importing only the factorial() method from the math library.

# import factorial() method 
# of math library inside this 
# program
from math import factorial

# given input
number = 5

# call factorial() method of 
# math library and then print
# the result
print("Factorial of", number, 
      ":", factorial(number))

Output:

Factorial of 5 : 120

Code 3: Using iterative approach.

# given input
number = 6

# factorial of 0 is 1
if number == 0 :
    factorial = 1

else:
    factorial = number

# reverse looping form number - 1
# upto 2
for value in range(number - 1, 1, -1):
    
    # multiplying number one by one 
    # in each iteration
    factorial *= value
    
# showing final result 
print("Factorial of", number, 
      ":", factorial)

Output:

Factorial of 6 : 720

Code 4: By Creating user-defined function then applying iterative approach.

# Create a user-defined function
# for finding factorial of
# a given number
def findFactorial(number):
    
    # when number is either 0 or 1 
    # then simply return it
    if (number == 0 or number == 1):
        return number
    
    factorial = number

    # reverse looping form number - 1
    # upto 2
    for value in range(number - 1, 1, -1):
        factorial *= value

    return factorial

# main code
if __name__ == "__main__" :
    
    # taking input from user and
    # convert it into integer
    number = int(input("Enter a Number: "))

    # function calling and printing
    print("Factorial of", number, 
          ":", findFactorial(number))

Output:

Enter a Number: 7
Factorial of 7 : 5040

Code 5: By Creating user-defined function then applying Recursive approach.

# Create a user-defined function
# for finding factorial of
# a given number

# recursive approach
def findFactorial(number):
    
    # when number becomes 0 or 1 
    # then simply return it
    if (number == 0 or number == 1) :
        return 1
    
    # otherwise recursively compute this
    else:
        return number * findFactorial(number - 1)
    
# main code 
if __name__ == "__main__" :
    
    # taking input from user and
    # convert it into integer
    number = int(input("Enter a Number: "))
    
    # function calling and printing
    print("Factorial of", number, 
          ":", findFactorial(number))

Output:

Enter a Number: 7
Factorial of 7 : 5040

Code 6: By Creating user-defined function then applying recursive approach along with the use of the ternary operator.

# Create a user-defined function
# for finding factorial of
# a given number

# recursive approach
def findFactorial(number):

    # use of ternary operator
    
    # if number is either 0 
    # or 1 then return 1
    # otherwise recursively
    # calling function
    return 1 if number == 0 or number == 1 else number * findFactorial(number - 1)

# main code
if __name__ == "__main__" :
    
    # taking input from user and
    # convert it into integer
    number = int(input("Enter a Number: "))
    
    # function calling and printing
    print("Factorial of", number, 
          ":", findFactorial(number))

Output:

Enter a Number: 6
Factorial of 6 : 720