• Source 
    1. def factorial(n):
    2.   """
    3.   This function calculates the factorial of a non-negative integer.
    4.  
    5.   Args:
    6.     n: The non-negative integer for which to calculate the factorial.
    7.  
    8.   Returns:
    9.     The factorial of n, or 1 if n is 0.
    10.     Raises ValueError if n is negative.
    11.   """
    12.   if n < 0:
    13.     raise ValueError("Factorial is not defined for negative numbers")
    14.   elif n == 0:
    15.     return 1
    16.   else:
    17.     result = 1
    18.     for i in range(1, n + 1):
    19.       result *= i
    20.     return result
    21.  
    22. # Example usage:
    23. number = 5
    24. fact = factorial(number)
    25. print(f"The factorial of {number} is {fact}")