argcomplete - Bash tab completion for argparse

Tab complete all the things!

Argcomplete provides easy, extensible command line tab completion of arguments for your Python script.

It makes two assumptions:

• You're using bash or zsh as your shell
• You're using argparse to manage your command line arguments/options

Argcomplete is particularly useful if your program has lots of options or subparsers, and if your program can dynamically suggest completions for your argument/option values (for example, if the user is browsing resources over the network).

Installation

pip install argcomplete
activate-global-python-argcomplete

See Activating global completion below if the second step reports an error.

Refresh your bash environment (start a new shell or source /etc/profile).

Synopsis

Python code (e.g. my-awesome-script.py):

#!/usr/bin/env python
# PYTHON_ARGCOMPLETE_OK
import argcomplete, argparse
parser = argparse.ArgumentParser()
...
argcomplete.autocomplete(parser)
args = parser.parse_args()
...

Shellcode (only necessary if global completion is not activated - see Global completion below), to be put in e.g. .bashrc:

eval "$(register-python-argcomplete my-awesome-script.py)"

argcomplete.autocomplete(parser)

This method is the entry point to the module. It must be called after ArgumentParser construction is complete, but before the ArgumentParser.parse_args() method is called. The method looks for an environment variable that the completion hook shellcode sets, and if it's there, collects completions, prints them to the output stream (fd 8 by default), and exits. Otherwise, it returns to the caller immediately.

Side effects

Argcomplete gets completions by running your program. It intercepts the execution flow at the moment argcomplete.autocomplete() is called. After sending completions, it exits using exit_method (os._exit by default). This means if your program has any side effects that happen before argcomplete is called, those side effects will happen every time the user presses <TAB> (although anything your program prints to stdout or stderr will be suppressed). For this reason it's best to construct the argument parser and call argcomplete.autocomplete() as early as possible in your execution flow.

Specifying completers

You can specify custom completion functions for your options and arguments. Two styles are supported: callable and readline-style. Callable completers are simpler. They are called with the following keyword arguments:

• prefix: The prefix text of the last word before the cursor on the command line. All returned completions should begin with this prefix.
• action: The argparse.Action instance that this completer was called for.
• parser: The argparse.ArgumentParser instance that the action was taken by.
• parsed_args: The result of argument parsing so far (the argparse.Namespace args object normally returned by ArgumentParser.parse_args()).

Completers should return their completions as a list of strings. An example completer for names of environment variables might look like this:

def EnvironCompleter(prefix, **kwargs):
    return (v for v in os.environ if v.startswith(prefix))

To specify a completer for an argument or option, set the completer attribute of its associated action. An easy way to do this at definition time is:

from argcomplete.completers import EnvironCompleter

parser = argparse.ArgumentParser()
parser.add_argument("--env-var1").completer = EnvironCompleter
parser.add_argument("--env-var2").completer = EnvironCompleter
argcomplete.autocomplete(parser)

If you specify the choices keyword for an argparse option or argument (and don't specify a completer), it will be used for completions.

A completer that is initialized with a set of all possible choices of values for its action might look like this:

class ChoicesCompleter(object):
    def __init__(self, choices=[]):
        self.choices = choices

    def __call__(self, prefix, **kwargs):
        return (c for c in self.choices if c.startswith(prefix))

The following two ways to specify a static set of choices are equivalent for completion purposes:

from argcomplete.completers import ChoicesCompleter

parser.add_argument("--protocol", choices=('http', 'https', 'ssh', 'rsync', 'wss'))
parser.add_argument("--proto").completer=ChoicesCompleter(('http', 'https', 'ssh', 'rsync', 'wss'))

The following script uses parsed_args and Requests to query GitHub for publicly known members of an organization and complete their names, then prints the member description:

#!/usr/bin/env python
# PYTHON_ARGCOMPLETE_OK
import argcomplete, argparse, requests, pprint

def github_org_members(prefix, parsed_args, **kwargs):
    resource = "https://api.github.com/orgs/{org}/members".format(org=parsed_args.organization)
    return (member['login'] for member in requests.get(resource).json() if member['login'].startswith(prefix))

parser = argparse.ArgumentParser()
parser.add_argument("--organization", help="GitHub organization")
parser.add_argument("--member", help="GitHub member").completer = github_org_members

argcomplete.autocomplete(parser)
args = parser.parse_args()

pprint.pprint(requests.get("https://api.github.com/users/{m}".format(m=args.member)).json())

Try it like this:

./describe_github_user.py --organization heroku --member <TAB>

Readline-style completers

The readline module defines a completer protocol in rlcompleter. Readline-style completers are also supported by argcomplete, so you can use the same completer object both in an interactive readline-powered shell and on the bash command line. For example, you can use the readline-style completer provided by IPython to get introspective completions like you would get in the IPython shell:

import IPython
parser.add_argument("--python-name").completer = IPython.core.completer.Completer()

Printing warnings in completers

Normal stdout/stderr output is suspended when argcomplete runs. Sometimes, though, when the user presses <TAB>, it's appropriate to print information about why completions generation failed. To do this, use warn:

from argcomplete import warn

def AwesomeWebServiceCompleter(prefix, **kwargs):
    if login_failed:
        warn("Please log in to Awesome Web Service to use autocompletion")
    return completions

Global completion

In global completion mode, you don't have to register each argcomplete-capable executable separately. Instead, bash will look for the string PYTHON_ARGCOMPLETE_OK in the first 1024 bytes of any executable that it's running completion for, and if it's found, follow the rest of the argcomplete protocol as described above.

Bash version compatibility

Global completion requires bash support for complete -D, which was introduced in bash 4.2. On older systems, you will need to update bash to use this feature. Check the version of the running copy of bash with echo $BASH_VERSION.

Note

If you use setuptools/distribute scripts or entry_points directives to package your module, argcomplete will follow the wrapper scripts to their destination and look for PYTHON_ARGCOMPLETE_OK in the destination code.

Activating global completion

The script activate-global-python-argcomplete will try to install the file bash_completion.d/python-argcomplete.sh (see on GitHub) into an appropriate location on your system (/etc/bash_completion.d/ or ~/.bash_completion.d/). If it fails, but you know the correct location of your bash completion scripts directory, you can specify it with --dest:

activate-global-python-argcomplete --dest=/path/to/bash_completion.d

Otherwise, you can redirect its shellcode output into a file:

activate-global-python-argcomplete --dest=- > file

The file's contents should then be sourced in e.g. ~/.bashrc.

Acknowledgments

Inspired and informed by the optcomplete module by Martin Blais.

Links

• Project home page (GitHub)
• Documentation (Read the Docs)
• Package distribution (Crate) (PyPI)

Bugs

Please report bugs, issues, feature requests, etc. on GitHub.

License

Licensed under the terms of the Apache License, Version 2.0.