File Encryption Tool in Python

# This program reads a text file, encodes the content using a simple Caesar Cipher, 
# and writes the encoded content to a new file.

def encode_text(input_filename, shift=3):
    try:
        # Open the input file in read mode
        with open(input_filename, 'r') as infile:
            # Read the content of the file
            content = infile.read()

        # Initialize the encoded content
        encoded_content = ''
        
        # Encode each character in the content
        for char in content:
            if char.isalpha():  # Check if the character is a letter
                # Shift the character and handle both lowercase and uppercase letters
                shift_base = 65 if char.isupper() else 97
                encoded_char = chr((ord(char) - shift_base + shift) % 26 + shift_base)
                encoded_content += encoded_char
            else:
                # If the character is not a letter, keep it unchanged
                encoded_content += char

        # Create a new file name by adding ".encoded" extension
        output_filename = input_filename + ".encoded"

        # Open the output file in write mode
        with open(output_filename, 'w') as outfile:
            # Write the encoded content to the new file
            outfile.write(encoded_content)

        print(f"File has been successfully encoded and saved as {output_filename}.")
    
    except FileNotFoundError:
        print(f"The file {input_filename} does not exist.")
    except Exception as e:
        print(f"An error occurred: {e}")

# Example usage
input_file = "example.txt"  # Replace with your input file name
encode_text(input_file)

 Output

If the example.txt file contains:

Hello, this is a secret message.

After running the program with a shift of 3, the example.txt.encoded file will contain:

Khoor, wklv lv d vhfuhw phvvdjh.