Write a simple Python module that solves a problem.

Answer 1

Sure! Let's create a simple Python module that provides a function to calculate the factorial of a number. The factorial of a non-negative integer \( n \) is the product of all positive integers less than or equal to \( n \). It's commonly used in mathematics, particularly in combinatorics.

Here's how we can implement this:

Step 1: Create the Module

You can create a new file named factorial.py for your module. Here is the code for the module:

# factorial.py

def factorial(n):
    """
    Returns the factorial of a non-negative integer n.

    Parameters:
    n (int): A non-negative integer

    Returns:
    int: The factorial of n
    """
    if n < 0:
        raise ValueError("Factorial is not defined for negative numbers.")
    elif n == 0 or n == 1:
        return 1
    else:
        result = 1
        for i in range(2, n + 1):
            result *= i
        return result

Step 2: Using the Module

You can now use this module in another Python script. Create a new file named main.py and include the following code:

# main.py

from factorial import factorial

def main():
    number = int(input("Enter a non-negative integer: "))
    try:
        result = factorial(number)
        print(f"The factorial of {number} is {result}")
    except ValueError as e:
        print(e)

if __name__ == "__main__":
    main()

Explanation

1. factorial.py:

   • Contains a single function factorial which computes the factorial.
   • The function raises a ValueError if a negative integer is passed.
   • The factorial is calculated iteratively.

2. main.py:

   • Imports the factorial function from the factorial module.
   • Asks the user for a non-negative integer, computes its factorial, and prints the result.
   • Catches any potential exceptions (like entering a negative number) and prints the error message.

Running the Code

To run the program, make sure both factorial.py and main.py are in the same directory. Run the main.py script, and it will prompt you to enter a non-negative integer, then it will display the factorial.

$ python main.py
Enter a non-negative integer: 5
The factorial of 5 is 120

That's it! You now have a simple Python module to calculate factorials.