argparse

library1.4.0pypypi✓ verified 25d ago

argparse is Python's standard library module for parsing command-line arguments. It simplifies the creation of user-friendly command-line interfaces by allowing programs to define required arguments and options, automatically generating help messages, and handling argument parsing and validation. It has been part of the standard library since Python 2.7 and 3.2. The PyPI package (version 1.4.0) is a backport primarily for older Python versions (< 2.7 or < 3.2) and is currently archived.

devops

pip install argparse

github ↗package ↗

INSTALL

IMPORT

SIG · ARGPARSE

argparse

devopspythonv1.4.0

Install

1.6s avg

Import

10ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v1.4.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.006s · 17.9MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.6s · import 0.004s · 18MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

argparse

✓ import argparse

This quickstart defines a basic command-line tool that takes a required 'name' argument and an optional '--verbose' flag. It demonstrates creating an `ArgumentParser`, adding arguments, and parsing them.

import argparse def main(): parser = argparse.ArgumentParser( description='A simple command-line tool.' ) parser.add_argument( 'name', type=str, help='The name to greet.' ) parser.add_argument( '-v', '--verbose', action='store_true', help='Enable verbose output.' ) args = parser.parse_args() if args.verbose: print(f"Verbose mode enabled. Greeting {args.name}...") print(f"Hello, {args.name}!") if __name__ == '__main__': main()

Debug

Known issues

gotchaThe `argparse` module is part of the Python standard library for versions 2.7 and 3.2 and later. The PyPI package `argparse` (version 1.4.0) is a backport primarily intended for older Python versions (e.g., Python < 2.7 or < 3.2) or specific older Python 3.x releases. For most modern Python users, `pip install argparse` is unnecessary and potentially problematic as you already have a built-in, possibly newer, version.

fix

Do not `pip install argparse` on modern Python versions; simply `import argparse`. If targeting older Python versions, explicitly install the PyPI backport.

affects: <= 1.4.0 (PyPI package) on Python >= 2.7 or >= 3.2

gotchaBy default, `argparse` treats all command-line inputs as strings. If you expect integer, float, or other types, you must explicitly specify the `type` argument in `add_argument()`. Failure to do so will result in string values, requiring manual conversion and validation in your code.

fix

Use `parser.add_argument('arg_name', type=int, help='...')` or `type=float` for automatic type conversion and basic validation.

affects: All versions

gotchaWhen `argparse` encounters invalid arguments or requests for help, its default behavior is to print messages to `sys.stderr` and then exit the program using `sys.exit()`. This can be undesirable in applications where you want to handle errors programmatically or integrate argument parsing into a larger system without exiting.

fix

To customize this behavior, you can subclass `ArgumentParser` and override the `exit()` or `_print_message()` methods. Alternatively, for simple cases, `parser.parse_args(args=['--help'])` will still exit, but `parser.parse_known_args()` can be used to process only recognized arguments and return the rest.

affects: All versions

deprecatedThe `nargs=REMAINDER` action was removed from the official documentation due to its fragility and potential for unexpected behavior when interspersed with other options. While still functional, it's not recommended for new code.

fix

Instead of `nargs=REMAINDER`, consider using `parser.parse_known_args()` to separate known arguments from unrecognized ones, and then process the 'unknown' arguments manually if needed.

affects: Python 3.9+ documentation (removed from docs, still functions)

breakingThe `optparse` module, a predecessor to `argparse`, was officially deprecated in Python 2.7+ and 3.2+ in favor of `argparse`. While `optparse` is still available, `argparse` offers more features and a different API, meaning direct replacements might require code changes.

fix

New projects should use `argparse`. For existing `optparse` code, review the 'Upgrading Optparse Code' section in the `argparse` documentation for migration guidance, as direct compatibility is not always maintained.

affects: Python 2.7, 3.2 and later (deprecation of optparse)

gotchaIf an argument value itself starts with a hyphen (e.g., a negative number or a filename like `-output.txt`), `argparse` might misinterpret it as an optional argument or flag, leading to 'unrecognized argument' errors.

fix

Users can typically resolve this by preceding such values with a special `--` argument, which tells `argparse` to stop processing options and treat everything that follows as positional arguments. For specific arguments, you can also adjust `parser.prefix_chars` if appropriate, or use `nargs` and a custom type if dealing with very specific formats.

affects: All versions

gotchaWhen a required argument (especially positional arguments without `nargs='?'` or `default`) is not provided on the command line, `argparse` will raise an error and exit, indicating which arguments are missing. This is its intended behavior for enforcing argument presence.

fix

Ensure all required arguments are provided when invoking the script. For optional positional arguments, use `nargs='?'` or provide a `default` value in `add_argument()`.

affects: All versions

gotchaWhen a positional argument is defined in `argparse` without `nargs='?'` or a `default` value, it becomes a required argument. If such an argument is omitted from the command line, `argparse` will raise an error indicating that the argument is required and then exit.

fix

Ensure all required positional arguments are provided on the command line. If an argument should be optional, define it with `nargs='?'` or provide a `default` value.

affects: All versions

Errors

Common errors & fixes

error: argument N: invalid int value: 'a'

Occurs when a non-integer value is provided for an argument expected to be an integer.

fix

Ensure that all inputs for integer arguments are valid integers.

error: unrecognized arguments: --unknown

Happens when an argument is passed that the parser does not recognize.

fix

Verify that all provided arguments are defined in the parser and correctly spelled.

error: the following arguments are required: --input

Triggered when a required argument is missing from the command line input.

fix

Include all required arguments when running the program.

error: argument --mode: invalid choice: 'fast' (choose from 'slow', 'medium')

Occurs when an argument is given a value that is not among its predefined choices.

fix

Provide a value that is within the allowed choices for the argument.

error: argument --count: invalid int value: 'ten'

Happens when a non-integer string is provided for an argument that expects an integer.

fix

Ensure that the value provided for the argument is a valid integer.

Upgrade

Version history

1.4.0latest on PyPI · released Sep 14, 2015

Audit

Dependencies

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Agent activity

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Resources

githubhttps://github.com/ThomasWaldmann/argparse ↗

packagehttps://pypi.org/project/argparse/ ↗