Yaargh: Yet Another Argh

Yaargh is a fork of Argh (https://github.com/neithere/argh/).

Why fork?

The argh project is no longer maintained (neithere#124 (comment)). This project will attempt to fix issues and make improvements to the original project. The intent is for all these changes to be made back to the original argh project when that becomes possible, and for yaargh to act as a replacement until it is.

You can use yaargh as a drop-in replacement for argh (import yaargh as argh) though see Compatability below.

In order to support using yaargh automatically even in applications where you can't easily change the code, the optional feature yaargh[import-argh] will add a dummy argh module such that import argh will use yaargh.

Highlights

The most signifigant differences from argh, and reasons you may prefer to use it:

• Commands that fail with a CommandError now exit with status 1 (failure) instead of status 0 (success). This is extremely important when used in scripts.

Compatability

While yaargh strives to maintain backwards compatability with argh and its existing behavior, the nature of a library like argh with a large amount of "magic" behavior and defaults means that what we consider the best default may change from version to version. For example, help text wording may change.

In addition, there is behavior that is almost always a bug but that it is technically possible some users rely on.

Both kinds of compatability breaks are listed below:

• If a function's type signature included a *varargs argument with an annotation of type str, this annotation previously was ignored. Now, that annotation will be used as a help string. In almost all cases this should be fixing behavior to match user intent, but it will technically result in different --help output.
• Previously, if a function raised a yaargh.CommandError or an error explicitly marked as wrapped, then yaargh.dispatch() (and by extension yaargh.dispatch_command() and yaargh.dispatch_commands()) would write the error message to the given error_file (by default sys.stderr), then return. It now raises a SystemExit instead of returning. In almost all cases, dispatch() is the last thing the program does anyway, and parsing failures already caused a SystemExit to be raised so most users who need to do something after error will already be catching it. This is a signifigant break but is nessecary to allow non-zero exit codes for failed commands.
• Related to the above, commands that fail with a yaargh.CommandError or other wrapped error will now exit with status 1, indicating failure. Previously, unless the user did something to avoid it, the command would have returned from yaargh.dispatch() and subsequently exited success. In the vast majority of cases this would have been a latent bug likely to cause havoc in scripts or other systems which rely on status code to check if a command succeeded. You can use CommandError(message, code=0) to restore the previous behavior.

Original README

Building a command-line interface? Found yourself uttering "argh!" while struggling with the API of argparse? Don't like the complexity but need the power?

Everything should be made as simple as possible, but no simpler.

—Albert Einstein (probably)

Argh is a smart wrapper for argparse. Argparse is a very powerful tool; Argh just makes it easy to use.

In a nutshell

Argh-powered applications are simple but flexible:

Modular:	Declaration of commands can be decoupled from assembling and dispatching;
Pythonic:	Commands are declared naturally, no complex API calls in most cases;
Reusable:	Commands are plain functions, can be used directly outside of CLI context;
Layered:	The complexity of code raises with requirements;
Transparent:	The full power of argparse is available whenever needed;
Namespaced:	Nested commands are a piece of cake, no messing with subparsers (though they are of course used under the hood);
Term-Friendly:	Command output is processed with respect to stream encoding;
Unobtrusive:	Argh can dispatch a subset of pure-argparse code, and pure-argparse code can update and dispatch a parser assembled with Argh;
DRY:	The amount of boilerplate code is minimal; among other things, Argh will: infer command name from function name; infer arguments from function signature; infer argument type from the default value; infer argument action from the default value (for booleans); add an alias root command help for the --help argument.
NIH free:	Argh supports completion, progress bars and everything else by being friendly to excellent 3rd-party libraries. No need to reinvent the wheel.

Sounds good? Check the tutorial!

Relation to argparse

Argh is fully compatible with argparse. You can mix Argh-agnostic and Argh-aware code. Just keep in mind that the dispatcher does some extra work that a custom dispatcher may not do.

Installation

Using pip:

$ pip install argh

Arch Linux (AUR):

$ yaourt python-argh

Examples

A very simple application with one command:

import argh

def main():
    return 'Hello world'

argh.dispatch_command(main)

Run it:

$ ./app.py
Hello world

A potentially modular application with multiple commands:

import argh

# declaring:

def echo(text):
    "Returns given word as is."
    return text

def greet(name, greeting='Hello'):
    "Greets the user with given name. The greeting is customizable."
    return greeting + ', ' + name

# assembling:

parser = argh.ArghParser()
parser.add_commands([echo, greet])

# dispatching:

if __name__ == '__main__':
    parser.dispatch()

Of course it works:

$ ./app.py greet Andy
Hello, Andy

$ ./app.py greet Andy -g Arrrgh
Arrrgh, Andy

Here's the auto-generated help for this application (note how the docstrings are reused):

$ ./app.py help

usage: app.py {echo,greet} ...

positional arguments:
    echo        Returns given word as is.
    greet       Greets the user with given name. The greeting is customizable.

...and for a specific command (an ordinary function signature is converted to CLI arguments):

$ ./app.py help greet

usage: app.py greet [-g GREETING] name

Greets the user with given name. The greeting is customizable.

positional arguments:
  name

optional arguments:
  -g GREETING, --greeting GREETING   'Hello'

(The help messages have been simplified a bit for brevity.)

Argh easily maps plain Python functions to CLI. Sometimes this is not enough; in these cases the powerful API of argparse is also available:

@arg('text', default='hello world', nargs='+', help='The message')
def echo(text):
    print text

The approaches can be safely combined even up to this level:

# adding help to `foo` which is in the function signature:
@arg('foo', help='blah')
# these are not in the signature so they go to **kwargs:
@arg('baz')
@arg('-q', '--quux')
# the function itself:
def cmd(foo, bar=1, *args, **kwargs):
    yield foo
    yield bar
    yield ', '.join(args)
    yield kwargs['baz']
    yield kwargs['quux']

Links

• Project home page (GitHub)
• Documentation (Read the Docs)
• Package distribution (PyPI)
• Questions, requests, bug reports, etc.:
  • Issue tracker (GitHub)
  • Mailing list (subscribe to get important announcements)
  • Direct e-mail (neithere at gmail com)

Author

Developed by Andrey Mikhaylenko since 2010.

See file AUTHORS for a complete list of contributors to this library.

Support

The fastest way to improve this project is to submit tested and documented patches or detailed bug reports.

Otherwise you can "flattr" me:

Licensing

Argh is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Argh is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with Argh. If not, see <http://gnu.org/licenses/>.