arichardson/argcomplete

Python and tab completion, better together.

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 as your shell (limited support for zsh and tcsh is available)
• 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 for details about the second step (or if it 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.

Performance

If the program takes a long time to get to the point where argcomplete.autocomplete() is called, the tab completion process will feel sluggish, and the user may lose confidence in it. So it's also important to minimize the startup time of the program up to that point (for example, by deferring initialization or importing of large modules until after parsing options).

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 = [str(choice) for choice in 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'))

Note that if you use the choices=<completions> option, argparse will show all these choices in the --help output by default. To prevent this, set metavar (like parser.add_argument("--protocol", metavar="PROTOCOL", choices=('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>

If you have a useful completer to add to the completer library, send a pull request!

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()

You can also use argcomplete.CompletionFinder.rl_complete to plug your entire argparse parser as a readline 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

Using a custom completion validator

By default, argcomplete validates your completions by checking if they start with the prefix given to the completer. You can override this validation check by supplying the validator keyword to argcomplete.autocomplete():

def my_validator(current_input, keyword_to_check_against):
    # Pass through ALL options even if they don't all start with 'current_input'
    return True

argcomplete.autocomplete(parser, validator=my_validator)

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 OS X or older Linux systems, you will need to update bash to use this feature. Check the version of the running copy of bash with echo $BASH_VERSION. On OS X, install bash via Homebrew (brew install bash), add /usr/local/bin/bash to /etc/shells, and run chsh to change your shell.

Global completion is not currently compatible with zsh.

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.

Tcsh Support

To activate completions for tcsh use:

eval `register-python-argcomplete --shell tcsh my-awesome-script.py`

The python-argcomplete-tcsh script provides completions for tcsh. The following is an example of the tcsh completion syntax for my-awesome-script.py emitted by register-python-argcomplete:

complete my-awesome-script.py 'p@*@`python-argcomplete-tcsh my-awesome-script.py`@'

Debugging

Set the _ARC_DEBUG variable in your shell to enable verbose debug output every time argcomplete runs. Alternatively, you can bypass the bash completion shellcode altogether, and interact with the Python code directly with something like this:

PROGNAME=./{YOUR_PY_SCRIPT} TEST_ARGS='some_arguments with autocompl' _ARC_DEBUG=1 COMP_LINE="$PROGNAME $TEST_ARGS" COMP_POINT=31 _ARGCOMPLETE=1 $PROGNAME 8>&1 9>>~/autocomplete_debug.log

Then tail:

tail -f ~/autocomplete_debug.log

Acknowledgments

Inspired and informed by the optcomplete module by Martin Blais.

Links

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

Bugs

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

License

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