Write a Python function to calculate the factorial of a number. -

Calculating the factorial of a number is a common task in mathematics and programming. The factorial of a non-negative integer ( n ) is the product of all positive integers less than or equal to ( n ). For example, the factorial of 5 (denoted as ( 5! )) is ( 5 \times 4 \times 3 \times 2 \times 1 = 120 ).

In this article, we will explore how to write a Python function to calculate the factorial of a number. We’ll keep things simple, unique, and SEO-friendly, ensuring that anyone can follow along.

What is a Factorial?

The factorial of a number ( n ) can be defined as:

( n! = n \times (n – 1) \times (n – 2) \times … \times 1 ) for ( n > 0 )
( 0! = 1 ) (by definition)

Python Function to Calculate Factorial

To calculate the factorial of a number in Python, we can use both iterative and recursive approaches. Here, we will demonstrate both methods.

Iterative Approach

In the iterative approach, we use a loop to multiply numbers from 1 to ( n ).

Here’s how to implement this in Python:

def factorial_iterative(n):
    if n < 0:
        return "Factorial is not defined for negative numbers."
    result = 1
    for i in range(1, n + 1):
        result *= i
    return result

Recursive Approach

The recursive approach involves the function calling itself. This method is more elegant but can be less efficient for large numbers due to Python’s recursion limit.

Here’s the recursive implementation:

def factorial_recursive(n):
    if n < 0:
        return "Factorial is not defined for negative numbers."
    if n == 0:
        return 1
    return n * factorial_recursive(n - 1)

How to Use the Functions

You can use either of these functions to calculate the factorial of a number. Here’s an example of how to call these functions:

number = 5
print("Iterative Factorial of", number, "is", factorial_iterative(number))
print("Recursive Factorial of", number, "is", factorial_recursive(number))

Output

When you run the code above with the number set to 5, you will see:

Iterative Factorial of 5 is 120
Recursive Factorial of 5 is 120

Conclusion

Calculating the factorial of a number is a straightforward task in Python. Whether you choose the iterative or recursive approach, both methods provide an efficient way to compute the factorial. Remember, the factorial is only defined for non-negative integers, so always handle negative inputs appropriately.

By following this guide, you should now be able to write a Python function that calculates the factorial of any non-negative integer. This knowledge is useful in various fields, including mathematics, computer science, and statistics.

Key Takeaways

The factorial of a number is the product of all positive integers up to that number.
You can calculate factorials using both iterative and recursive methods in Python.
Always handle negative input gracefully by providing an informative message.

Now, go ahead and implement your own factorial function in Python, and enjoy the power of programming!