How Do You Write A Factorial Program In Python?

Q: What is the logic of factorial?

In factorial, a function keeps on multiplying a number by every number which is less than it till it becomes less than 1. For Example, the factorial of a number 4 is found by multiplying 4,3,2 and 1, i,e. 4! = 4 x 3 x 2 x 1 = 24 which is equal to 24.

Q: Why is zero factorial 1?

Factorial can only be calculated for positive integers but as there are no positive integer values less than zero. Data cannot be arranged which counts as the possible combination of data arrangement.

Q: What is an example of a factorial?

Consider the factorial of a number 4 is found by multiplying 4,3,2 and 1, i,e. 4! = 4 x 3 x 2 x 1 = 24 which is equal to 24.

Factorial program in Python helps to calculate the factorial of a number using the Python programming language. Nowadays, Python is one of the most widely used among developers worldwide due to its easy-to-learn and code syntax. It consists of an extensive set of libraries and frameworks to help you perform various operations effectively. Read the complete article to learn how to write a factorial program in Python.

Table of Contents

What is the Factorial of a Number?

Factorial of a number ‘n’ is defined as the product of that number with every whole number less than or equal to ‘n’ till 1.

Factorial of a number is a function which multiplies a number by every number less than it or below it till 1. For Example, the factorial of a number 4 is found by multiplying 4,3,2 and 1, i,e. 4! = 4 x 3 x 2 x 1 = 24 which is equal to 24.

Algorithm for Factorial Program in Python

Let us check a recursive algorithm for finding the factorial of a number using Python.

Step1: Start
Step 2: Declare a variable n, fact, and i.
Step 3: Now, read the input number given by the user.
Step 4: Initialize variable fact with 1 and i with 1.
Step 5: Repeat until i<=number

fact = fact * i

I = i+1

Step 6: Print the value of fact
Step 7: End

Pseudocode for Factorial Program in Python

Let us check the pseudocode for finding the factorial of a number in Python.

Factorial Program in Python

Read the user input number

Fact = 1

i = 1

WHILE i< = number

Fact = Fact * i

i = i +1

END WHILE

PRINT Fact

Factorial Program in Python: Recursive Approach

Let us check the method to calculate factorial using recursive approach in the table below.

It is one of the most common factorial algorithm which breaks down the factorial into smaller subproblems until it reaches the base case. Check the recursive algorithm for factorial program.

Factorial Program in Python: Recursive Algorithm

function factorial (n) :

if n == 0

return 1

else:

return n * factorial (n-1)

Our base case will occur when the value of n becomes 0 then we return 1 otherwise we keep on multiplying by n and calling the function by n-1.

Implementation of Factorial Program in Python using Recursive Approach

Check the code implementation of factorial program in Python in the table below.

Factorial Program in Python: Recursive Algorithm

class Solution:

def factorial (self, N):

if(N==1):

return N

elif(N==0):

return 1

return N*self.factorial(N-1)

Factorial Program in Python: Iterative Approach

We can use iterative method to calculate large factorials efficiently. It also avoid the overhead which is caused by function call in recursive approach. It uses loops in place of function calls to calculate the factorial of a number.

Factorial Program in Python: Iterative Algorithm

function factorial (n):

result = 1

for i from 2 to n:

result *= i

return result;

First we initialize the variable result with 1.
Now, we will run a loop starting from 2 to the the number itself.
In each iteration, we keep on multiplying the result variable with the current integer i.
Finally, after the loops get over we return the result of the factorial n.

With iterative approach we can calculate factorial of a number more efficiently. Let us check the code for implementation of the iterative approach in Python.

Implementation of Factorial Program in Python using Iterative Approach

Let us check the iterative approach implementation using Python in the table below.

Factorial Program in Python: Iterative Algorithm

def factorial_iterative(n):

if n < 0:

return None

# Factorial is not defined for negative numbers

result = 1

for i in range(1, n + 1):

result *= i

return result

Factorial Program in Python: Which Approach is Better?

Let us check the the Difference between Recursive and iterative approach in the table below.

Difference between Recursive and Iterative Approach
Recursive Approach	Iterative Approach
In recursive approach, function calls itself directly or indirectly.	In iterative approach, loops are used to repeatedly execute a set of statements.
It break down the problem into subproblem and then calculate the factorial.	It uses single loop to find the factorial minimizing the risk of stack overflow.
This approach is poor for large factorials as it can be time consuming and inefficient because of the repeated function calls.	The iterative approach is efficient for large factorials.
It consists of overhead caused by recursive function calls.	It do not consists of overhead of recursive function calls.
It uses more memory.	It uses less memory.

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Factorial Program in Python FAQs

What is a factorial program in Python?

Factorial of a number ‘n’ is defined as the product of that number with every whole number less than or equal to ‘n’ till 1. We can calculate factorial using the Python programming language.

What is the logic of factorial?

In factorial, a function keeps on multiplying a number by every number which is less than it till it becomes less than 1. For Example, the factorial of a number 4 is found by multiplying 4,3,2 and 1, i,e. 4! = 4 x 3 x 2 x 1 = 24 which is equal to 24.

Why is zero factorial 1?

Factorial can only be calculated for positive integers but as there are no positive integer values less than zero. Data cannot be arranged which counts as the possible combination of data arrangement.