Introduction to Python Argparse

Argparse is a powerful library in Python used for creating command-line interfaces (CLI). It allows developers to specify what arguments a program requires and handles the parsing and processing of command-line arguments seamlessly.

Basic Usage of Argparse

To get started with argparse, you need to import the library and create an ArgumentParser object:

  
    import argparse
    parser = argparse.ArgumentParser(description='A simple argument parser example.')
  

Adding Arguments

Arguments can be added to the parser using the add_argument method:

  
    parser.add_argument('name', type=str, help='Name of the user')
    parser.add_argument('--age', type=int, help='Age of the user')
  

Parsing Arguments

Once arguments are added, you can parse them using the parse_args method:

  
    args = parser.parse_args()
    print(f'Name: {args.name}, Age: {args.age}')
  

Positional and Optional Arguments

Positional arguments are mandatory, while optional arguments are not. Optional arguments are usually prefixed with -- or -:

  
    parser.add_argument('filename', type=str, help='File to be processed')
    parser.add_argument('-v', '--verbose', action='store_true', help='Increase output verbosity')
  

Default Values

You can assign default values to arguments:

  
    parser.add_argument('--timeout', type=int, default=30, help='Timeout duration in seconds')
  

Mutually Exclusive Arguments

Argparse can handle mutually exclusive arguments using add_mutually_exclusive_group:

  
    group = parser.add_mutually_exclusive_group()
    group.add_argument('--quiet', action='store_true', help='Suppress output')
    group.add_argument('--debug', action='store_true', help='Enable debug mode')
  

Subparsers for Sub-Commands

Argparse supports sub-commands through subparsers:

  
    subparsers = parser.add_subparsers(dest='command')
    parser_a = subparsers.add_parser('command_a', help='Command A')
    parser_a.add_argument('--foo', type=int, help='Foo for Command A')
  

Complete Example CLI Application

Here is a complete example of a CLI application that utilizes many of argparse’s features:

  
    import argparse

    def main():
        parser = argparse.ArgumentParser(description='Example CLI application')
        parser.add_argument('username', type=str, help='Username for login')
        parser.add_argument('--password', type=str, help='Password for login')
        parser.add_argument('--verbose', '-v', action='store_true', help='Show detailed output')

        subparsers = parser.add_subparsers(dest='command', help='Available commands')

        user_parser = subparsers.add_parser('user', help='User-related commands')
        user_parser.add_argument('--create', action='store_true', help='Create a new user')
        user_parser.add_argument('--delete', type=int, help='Delete a user by ID')

        admin_parser = subparsers.add_parser('admin', help='Admin-related commands')
        admin_parser.add_argument('--ban', type=int, help='Ban a user by ID')

        args = parser.parse_args()

        if args.verbose:
            print('Verbose mode enabled')
        
        if args.command == 'user':
            if args.create:
                print(f'Creating user: {args.username}')
            elif args.delete:
                print(f'Deleting user ID: {args.delete}')
        elif args.command == 'admin':
            if args.ban:
                print(f'Banning user ID: {args.ban}')
        else:
            print(f'Username: {args.username}')
            if args.password:
                print(f'Password: {args.password}')

    if __name__ == '__main__':
        main()
  

In this example, the CLI application supports user login, verbosity, and sub-commands for user and admin operations.

This guide covers the essential aspects of argparse. By leveraging these features, you can efficiently build robust CLI applications.

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