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An astonishingly awesome application argument helper

Project description

Aaargh: an astonishingly awesome application argument helper.

Aaargh is a Python module that makes building friendly command line applications really easy. Applications built with Aaargh provide a single executable with a subcommand for each exposed Python function. Each subcommand may have its own command line arguments. This is similar to the way version control systems provide multiple commands using a single entry point. (Examples include bzr commit and git checkout).

Aaargh is named after one of the castles in the movie Monty Python and the Holy Grail. The acronym Aaargh stands for an astonishingly awesome application argument helper, but omits a few letters to make it triple A.

Aaargh is compatible with both Python 2.6+ and Python 3.


The Python standard library contains the optparse, getopt, and argparse modules, and out in the wild you will find many alternative command line interface libraries stacked on top of these, such as cliff, cement, opster, plac, and many others. Some of these libraries separate the command line interface setup of your application from the actual code, some force yet another argument parsing API upon you, some force you to hide your code in non-obvious framework constructs, and some even add dependencies on other modules.

This makes you scream aaargh. And, lo and behold, here it is!


Aaargh delegates almost all of its work to the argparse module, which does a great job handling arguments and printing usage information. However, argparse is a bit verbose and cumbersome for many simple applications, so Aaargh lets application authors minimize boilerplate code by wrapping commonly used argparse features in a few non-intrusive decorators. Aaargh does not hide the argparse API, since the decorators have exactly the same API as their argparse counterparts. This is a deliberate design decision, and this is what makes Aaargh different from its many alternatives.

The docstrings in the file contain all information you need to use Aaargh. Refer to the argparse documentation for information on specifying arguments, providing defaults, adding help texts, and so on.


A simple command line application that exposes a few functions looks like this:

#!/usr/bin/env python

import aaargh

app = aaargh.App(description="A simple greeting application.")

# Application level arguments:
app.arg('--name', help="Name of the person to greet", default="stranger")

# Application level defaults:
app.defaults(name="visitor")  # overrides "stranger"

def hello(name):  # application level "name" argument is always passed
    print("Hello, world!")

@app.cmd(name="hi", help="Say hi")  # override subcommand name
@app.cmd_arg('-r', '--repeat', type=int, default=1, help="How many times?")
def say_hi(name, repeat):  # both application and subcommand args
    for i in range(repeat):
        print("Hi, %s!" % name)

@app.cmd_defaults(name="my friend")  # overrides "visitor" for this command only
def greetings(name):
    print("Greetings, %s." % name)

if __name__ == '__main__':

The command line interface for this application behaves like this:

$ ./ hello
Hello, world!

$ ./ hi --repeat=3
Hi, visitor!
Hi, visitor!
Hi, visitor!

$ ./ --help
usage: [-h] [--name NAME] {hello,hi,greetings} ...

A simple greeting application.

optional arguments:
  -h, --help            show this help message and exit
  --name NAME           Name of the person to greet

    hi                  Say hi

$ ./ hi --help
usage: hi [-h] [-r REPEAT]

optional arguments:
  -h, --help            show this help message and exit
  -r REPEAT, --repeat REPEAT
                        How many times?


Installation using pip is trivial, especially when using virtualenv:

(yourenv) $ pip install aaargh

After succesful installation, this should work:

(yourenv) $ python
>>> import aaargh
>>> help(aaargh)


Version 0.6 (2014-02-16)

  • No longer use pbr for packaging (issue #12)

  • Add proper licensing file (issue #9)

  • Fix error message when calling the program without a subcommand under Python 3

Version 0.5 (2013-09-23)

  • No longer add global args to subcommands (issues #3 and #5)

  • Switch to pbr for packaging

Version 0.4 (2012-10-17)

  • Fix automatic argparse dependency installation when using pip install with Python 2.6.

Version 0.3 (2012-06-10)

  • Also accept global args after the subcommand

Version 0.2 (2012-05-17)

  • Add support for Python 3

Version 0.1 (2012-05-17)

  • Initial release

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