> For the complete documentation index, see [llms.txt](https://riteshs4hu.gitbook.io/infosec-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://riteshs4hu.gitbook.io/infosec-notes/language/python/library/argparse.md). # argparse `argparse` in Python is a powerful library for building command-line interfaces (CLIs). It simplifies the task of creating and handling command-line arguments, enabling users to provide inputs dynamically when running scripts. *** ### **Overview** 1. Define what arguments your program requires. 2. Parse command-line arguments automatically. 3. Generate helpful usage and error messages. #### **Key Components** 1. **ArgumentParser**: The main class for handling arguments. 2. **add\_argument()**: Method to define the arguments your program accepts. 3. **parse\_args()**: Method to process and retrieve the parsed arguments. *** ### **`ArgumentParser` Constructor Parameters** The `ArgumentParser` class defines the CLI behavior. Here are all its parameters: | **Parameter** | **Description** | **Default** | | ----------------------- | ----------------------------------------------------------------------------------------------- | ------------------------ | | `prog` | Program name (overrides the default, which is the script name). | `sys.argv[0]` | | `usage` | Custom usage message displayed in help or error messages. | Auto-generated usage | | `description` | Description of what the program does, displayed in the help message before the argument list. | `None` | | `epilog` | Text displayed after the argument help section in the help message. | `None` | | `parents` | A list of other `ArgumentParser` objects whose arguments should also be included. | `[]` | | `formatter_class` | Controls help message formatting. Common options: | `argparse.HelpFormatter` | | | - `RawDescriptionHelpFormatter` (preserves newlines). | | | | - `ArgumentDefaultsHelpFormatter` (shows default values). | | | `prefix_chars` | Characters used to prefix optional arguments (e.g., `-` or `/`). | `'-'` | | `fromfile_prefix_chars` | Characters that indicate a file containing arguments (e.g., `@`). | `None` | | `argument_default` | Global default value for arguments (overrides `None`). | `None` | | `conflict_handler` | Resolves argument conflicts (`'error'` or `'resolve'`). | `'error'` | | `add_help` | If `True`, adds the `-h/--help` argument automatically. | `True` | | `allow_abbrev` | If `True`, allows abbreviated forms of long options. | `True` | | `exit_on_error` | If `False`, raises exceptions instead of exiting on argument errors (introduced in Python 3.9). | `True` | *** ### **`add_argument` Parameters** The `add_argument` method defines what arguments your program accepts. It has the following parameters: | **Parameter** | **Description** | **Default** | | --------------- | ------------------------------------------------------------------------------------------------------ | ------------ | | `name_or_flags` | Positional argument name or optional flags (e.g., `'input_file'`, `'-v'`, `'--verbose'`). | **Required** | | `action` | Action to take when the argument is parsed: | `'store'` | | | - `'store'`: Save the provided value (default). | | | | - `'store_true'`: Save `True` if the flag is present (for booleans). | | | | - `'store_false'`: Save `False` if the flag is present (for booleans). | | | | - `'append'`: Add values to a list. | | | | - `'count'`: Count occurrences of the flag. | | | | - Custom action class. | | | `nargs` | Number of arguments to accept (e.g., `1`, `'?'`, `'*'`, `'+'`). | `None` | | `const` | A constant value assigned if the argument is used without a value (used with `nargs='?'` or `action`). | `None` | | `default` | Default value if the argument is not provided. | `None` | | `type` | The type to convert the argument to (e.g., `int`, `float`, `str`, or a custom callable). | `str` | | `choices` | A list of valid values for the argument (e.g., `[1, 2, 3]`). | `None` | | `required` | If `True`, makes the argument mandatory (only for optional arguments). | `False` | | `help` | A brief description of what the argument does (displayed in help messages). | `None` | | `metavar` | Custom name for the argument in usage and help messages. | `None` | | `dest` | The name of the attribute to store the value in (`args.dest`). | `None` | *** ### **Using `argparse`** Here’s a practical example of how to use `argparse`: ```python import argparse # Create a parser object parser = argparse.ArgumentParser( prog="example_program", usage="example_program [options] input_file", description="This program demonstrates argparse usage.", epilog="Thank you for using example_program!", ) # Define arguments parser.add_argument( 'input_file', # Positional argument type=str, help="The input file to process." ) parser.add_argument( '-v', '--verbose', # Optional argument action='store_true', help="Enable verbose mode." ) parser.add_argument( '--level', # Optional argument with choices type=int, choices=[1, 2, 3], default=1, help="Set the processing level (1, 2, or 3). Default is 1." ) # Parse arguments args = parser.parse_args() # Access arguments print(f"Input File: {args.input_file}") print(f"Verbose Mode: {args.verbose}") print(f"Processing Level: {args.level}") ``` *** ### **Features Summary** #### **Positional Arguments** * Required by default. * Example: ```python parser.add_argument('filename', type=str, help="Input file") ``` #### **Optional Arguments** * Start with `-` or `--`. * Example: ```python parser.add_argument('-v', '--verbose', action='store_true') ``` #### **Action Types** * `store`, `store_true`, `store_false`, `append`, `count`, custom. #### **Choices** * Restrict values to a predefined list: ```python parser.add_argument('--mode', choices=['fast', 'slow'], help="Execution mode") ``` #### **Default Values** * Provide a default: ```python parser.add_argument('--timeout', type=int, default=30, help="Timeout in seconds") ``` #### **Help and Formatting** * Automatically generates usage and help messages. *** ### **Complete Example** ```python import argparse # Initialize parser parser = argparse.ArgumentParser( prog="argparse_demo", description="Demonstrates argparse functionality", epilog="End of help message" ) # Add arguments parser.add_argument('input_file', type=str, help="File to process") parser.add_argument('-o', '--output', type=str, help="Output file") parser.add_argument('-v', '--verbose', action='store_true', help="Enable verbose mode") parser.add_argument('--level', type=int, choices=[1, 2, 3], default=1, help="Processing level (default: 1)") # Parse arguments args = parser.parse_args() # Use arguments print(f"Input File: {args.input_file}") print(f"Output File: {args.output}") print(f"Verbose Mode: {args.verbose}") print(f"Processing Level: {args.level}") ```