Factorial in Python

The best way to calculate Factorial in Python is using recursion function.

def factorial(number):
    # Check that the input is an integer before doing factorial math
    if not isinstance(number, int):
        raise TypeError("Sorry! Number must be an integer.")

    # Check if the input is a zero or a positive number
    if number < 0:
        raise ValueError("Sorry! Number must be zero or positive number.")

    def inner_factorial(number):
        # Base case: 0! and 1! are both 1
        if number <= 1:
            return 1

        # Recursive case: n! = n * (n - 1)!
        return number * inner_factorial(number - 1)

    # Start the recursive factorial calculation
    return inner_factorial(number)


# Print the factorial of 4.
print(factorial(4))

Output:

24