Command Line Arguments in Python

In Python, command-line arguments allow you to pass information to a Python script when running it from the command line or terminal. This is useful for making your script more dynamic and customizable without modifying the script itself.

Accessing Command-Line Arguments in Python:

Python provides the sys module to handle command-line arguments. Specifically, the sys.argv list holds the arguments passed to the script.

Syntax:

Steps to Use Command-Line Arguments:

1. Import the sys Module: You need to import sys to access sys.argv.
2. Run the Script with Arguments: When you run a Python script from the command line, you can pass additional arguments after the script name.

Example 1: Basic Example of Command-Line Arguments

Python Script (example.py):

How to run the script:

Output:

In this example, sys.argv contains a list where:

• sys.argv[0] is the name of the script (example.py),
• sys.argv[1:] contains the arguments passed after the script name (arg1, arg2, arg3).

Example 2: Using Command-Line Arguments in a Program

Here’s an example where we pass two numbers to the script and calculate their sum.

Python Script (sum.py):

How to run the script:

Output:

In this example:

• We use sys.argv[1] and sys.argv[2] to fetch the two command-line arguments.
• The script converts them to float to handle decimal numbers and calculates their sum.

Example 3: Using argparse Module for Advanced Argument Parsing

For more complex command-line parsing (e.g., flags, optional arguments), you can use the argparse module. This module provides a more structured way to handle arguments and automatically generates help messages.

Python Script (example_argparse.py):

How to run the script:

Output:

With argparse, you can also add optional arguments, set default values, and automatically generate usage help.

Key Features of argparse:

• Positional arguments: Arguments that are required and are passed in a specific order.
• Optional arguments: Arguments that are optional, typically with flags (e.g., -v or --verbose).
• Help messages: Automatically generated help and usage documentation.

For example:

This will display the automatically generated help message:

Summary:

• sys.argv: A simple way to access command-line arguments as a list.
• argparse: A powerful module for advanced command-line argument parsing, with features like help messages, optional arguments, and default values.

Using command-line arguments in Python makes your scripts more flexible and allows users to customize them without editing the code itself.