Python "argparse" library

Introduction to "argparse"

The argparse module, included in the Python standard library (since versions 2.7 and 3.2), is a powerful tool for creating user-friendly command-line interfaces (CLIs) for your Python scripts. It simplifies the process of parsing arguments passed from the command line, making your scripts more robust and easier to use.

Key Features:

• Flexibility: Defines various argument types (positional, optional, flags) and allows for multiple values.
• Error Handling: Catches invalid arguments and provides informative error messages.
• Help Messages: Generates usage and help messages automatically based on argument definitions.
• Subparsers: Enables creating complex CLIs with hierarchical structures.

Step by step Tutorial:

1 . Import the module:

import argparse

2 . Create an Argument Parser:

parser = argparse.ArgumentParser(description='Your script description')

3 . Define Arguments:
Positional arguments: Required arguments that appear in a specific order after the script name.

parser.add_argument('filename', help='The file to process')

Optional arguments: Added using flags (preceded by - or --) and can have default values.

parser.add_argument('-v', '--verbose', action='store_true', default=False,
                    help='Print verbose output')
parser.add_argument('-o', '--output', default='output.txt',
                    help='Output file (default: output.txt)')

• action='store_true': Sets a boolean flag (True if present, False otherwise).
• default='value': Provides a default value if the argument is not specified. Argument types: Control how arguments are interpreted. parser.add_argument('--age', type=int, help='Your age (as an integer)') parser.add_argument('--repeat', type=float, nargs=2, help='Repeat a value (takes two floating-point numbers)')
• type=int: Converts the argument value to an integer.
• nargs=2: Allows capturing multiple values for the argument. 4 . Parse Arguments:

args = parser.parse_args()

This captures the parsed arguments into a namespace object (args) that you can access in your script.


5 . Use the Arguments:

if args.verbose:
    print('Verbose mode enabled')

with open(args.filename, 'r') as f:
    # Process the file contents

if args.output:
    with open(args.output, 'w') as f:
        # Write output to the specified file

Complete Example:

import argparse

parser = argparse.ArgumentParser(description='Count lines in a file')
parser.add_argument('filename', help='The file to process')
parser.add_argument('-v', '--verbose', action='store_true', default=False,
                    help='Print detailed information')

args = parser.parse_args()

if args.verbose:
    print('Counting lines in:', args.filename)

with open(args.filename, 'r') as f:
    num_lines = sum(1 for _ in f)

print(f'The file {args.filename} has {num_lines} lines.')

Tips:

• Customize help messages using help arguments in add_argument
• Group related arguments using parser.add_argument_group()
• Create subparsers for complex CLIs with multiple commands using subparsers_action='store_subcommand'

By following these steps and exploring the advanced features of argparse, you can create robust, user-friendly, and well-documented command-line interfaces for your Python scripts.