Factorial of a non-negative number is defined as multiplication of all natural numbers smaller than it upto 1. For example – Factorial of -19 is not defined as its negative while factorial of 4 will be defined as 4 * 3 * 2 * 1 = 24. Quite simple just multiply **n(n-1)(n-2)(n-3)(n-4)………..upto 1** and you would get factorial of **number n**.

In this article, I’ll discuss algorithmic ways for implementing **Finding Factorial of a Number using Python Programming Language**. There can be three different approaches which can be used => **Recursion**, **Iteration** and **Using Python’s built-in methods**.

Let’s discuss each one of this algorithmic approach and put these together as Python Code for finding Factorial of Number.

Table of Contents

## Finding Factorial of a Number using Recursion

- Define number whose factorial to be calculated as num = 6
- Define a
**Python Function factorial(num)**which**recursively multiply num with num-1, num-2 up to 1**and returns final number - Final Number retuned by Function factorial(num) will be
**Factorial of number num**

Let’s put together all of these 3 steps as Python Code for Finding Factorial of a Number using Recursion.

```
# Find Factorial of a number using Recursion
# Define Number whose Factorial to be calculated
num = 6
def factorial(num):
# single line to find factorial
return 1 if (num==1 or num==0) else num * factorial(num - 1);
print("Factorial of",num,"is", factorial(num))
```

**Output of Above Code**

`Factorial of 6 is 720`

## Finding Factorial of a Number using Iterations

- Define Number whose Factorial need to be calculates as
**n = some_number** - Define a
**Python Function factorial(n)**which**iteratively multiply n with n-1, n-2 up to 1**and returns final number - Firstly
**Python Function factorial(n)**checks if n is less than 0, if so then return 0 otherwise checks if n is 0/1 if so then return 1 - Otherwise if n is neither 0/1 or less than 0 then use
**fact = 1**as a counter and iteratively numltiply it with n, n-1, n-2 up to 1. And then return**fact**, here**fact will be Factorial of number n**

Let’s put together all of these 4 steps as Python Code for finding factorial of a Number using Iterations.

```
# Python 3 program for finding Factorial using Recursion
# Define Number whose Factorial to be calculated
n = 9
def factorial(n):
if n < 0:
return 0
elif n == 0 or n == 1:
return 1
else:
fact = 1
while(n > 1):
fact *= n
n -= 1
return fact
print("Factorial of",n,"is =>",factorial(n))
```

**Output of Above Code**

`Factorial of 9 is => 362880`

## Finding Factorial of a Number using Built-in Functions

- Import Python’s math module into code using
**import math**statement - Define number whose factorial to be found as
**num = some_number** - Define
**Python Function factorial(num)**which takes in**num**and using**factorial function**from Math module calculates Factorial of num, then return it

```
# Pytho Program to Find factorial of a number using Built-in Functions
# Import Python's Math Module
import math
# Define Number whose Factorial to be Calculated
num = 8
def factorial(num):
return(math.factorial(num))
print("Factorial of", num, "is => ",factorial(num))
```

**Output of Above Code**

`Factorial of 8 is => 40320`

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