Building a Versatile File Processing CLI with Argparse

This challenge focuses on creating a command-line interface (CLI) application in Python that can perform basic operations on text files. You will use the argparse module to handle user inputs, making your script flexible and user-friendly. This skill is fundamental for automating tasks and building robust command-line tools.

Problem Description

Your task is to create a Python script that acts as a CLI tool for processing text files. The script should accept a filename as a required argument and then process the file based on optional arguments provided by the user.

Key Requirements:

1. Required Argument: The script must accept a single, mandatory argument: the path to the input text file.
2. Optional Arguments:
   • --count or -c: If present, the script should print the total number of lines in the file.
   • --words or -w: If present, the script should print the total number of words in the file. (A word is defined as a sequence of non-whitespace characters.)
   • --chars or -l: If present, the script should print the total number of characters in the file.
3. Combined Operations: The user should be able to combine multiple optional arguments. For example, they might request both line count and word count.
4. Default Behavior: If no optional arguments (--count, --words, --chars) are provided, the script should print the entire content of the file to standard output.
5. Error Handling:
   • If the specified input file does not exist, the script should print an informative error message and exit gracefully.
   • If an invalid argument is provided (e.g., --unknown-option), argparse should handle this by default.

Examples

Example 1:

Input:

python my_cli.py sample.txt

sample.txt content:

Hello world!
This is a test file.

Output:

Hello world!
This is a test file.

Explanation: No optional arguments were provided, so the script prints the entire content of sample.txt.

Example 2:

Input:

python my_cli.py sample.txt -c

sample.txt content:

Hello world!
This is a test file.

Output:

2

Explanation: The --count (or -c) argument was provided, so the script prints the number of lines in the file.

Example 3:

Input:

python my_cli.py sample.txt -c -w

sample.txt content:

Hello world!
This is a test file.

Output:

Lines: 2
Words: 8

Explanation: Both --count (-c) and --words (-w) arguments were provided. The output clearly labels each count.

Example 4:

Input:

python my_cli.py non_existent_file.txt -l

Output:

Error: File 'non_existent_file.txt' not found.

Explanation: The specified file does not exist, so an error message is printed, and the script exits.

Constraints

• The input filename will be a string representing a valid or invalid file path.
• The file contents will be standard UTF-8 encoded text.
• The number of lines, words, and characters will fit within standard integer types.
• The script should be written entirely in Python 3.
• The argparse module must be used for CLI argument parsing.

Notes

• Consider how you will handle line breaks when counting characters and words. A common approach is to count newline characters (\n) as part of the character count and to split lines by whitespace for word counting.
• When multiple optional arguments are present, you might want to format the output clearly, perhaps labeling each piece of information as shown in Example 3.
• The argparse module provides helpful built-in error messages for invalid arguments, but you'll need to implement custom logic for file-not-found errors.
• Think about how to efficiently read the file, especially for larger files, though performance is not a primary constraint here.