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, fish, and tcsh is available)
• You're using argparse <http://docs.python.org/3/library/argparse.html>_ 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

::

pip3 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):

.. code-block:: python

#!/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)"

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.

.. admonition:: 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.

.. admonition:: 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.
  For dynamic completers, this can be used to reduce the work required to generate possible completions.
* ``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:

.. code-block:: python

    def EnvironCompleter(**kwargs):
        return os.environ

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:

.. code-block:: python

    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:

.. code-block:: python

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

        def __call__(self, **kwargs):
            return self.choices

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

.. code-block:: python

    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 <https://raw.github.com/kislyuk/argcomplete/master/docs/examples/describe_github_user.py>`_ uses
``parsed_args`` and `Requests <http://python-requests.org/>`_ to query GitHub for publicly known members of an
organization and complete their names, then prints the member description:

.. code-block:: python

    #!/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 <https://raw.github.com/kislyuk/argcomplete/master/docs/examples/describe_github_user.py>`_ like this::

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

If you have a useful completer to add to the `completer library
<https://github.com/kislyuk/argcomplete/blob/master/argcomplete/completers.py>`_, 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:

.. _readline: http://docs.python.org/3/library/readline.html
.. _rlcompleter: http://docs.python.org/3/library/rlcompleter.html#completer-objects
.. _IPython: http://ipython.org/

.. code-block:: python

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

``argcomplete.CompletionFinder.rl_complete`` can also be used to plug in an 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``:

.. code-block:: python

    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():

.. code-block:: python

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.

Additionally, completion is activated for scripts run as python <script> and python -m <module>. This also works for alternate Python versions (e.g. python3 and pypy), as long as that version of Python has argcomplete installed.

.. admonition:: 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 <http://brew.sh/>_ (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.

If you choose not to use global completion, or ship a bash completion module that depends on argcomplete, you must register your script explicitly using eval "$(register-python-argcomplete my-awesome-script)". Standard bash completion registration roules apply: namely, the script name is passed directly to complete, meaning it is only tab completed when invoked exactly as it was registered. In the above example, my-awesome-script must be on the path, and the user must be attempting to complete it by that name. The above line alone would not allow you to complete ./my-awesome-script, or /path/to/my-awesome-script.

Activating global completion

The script ``activate-global-python-argcomplete`` will try to install the file
``bash_completion.d/python-argcomplete`` (`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``.

.. _`see on GitHub`: https://github.com/kislyuk/argcomplete/blob/master/argcomplete/bash_completion.d/python-argcomplete

Zsh Support
------------
To activate completions for zsh you need to have ``bashcompinit`` enabled in zsh::

    autoload -U bashcompinit
    bashcompinit

Afterwards you can enable completion for your scripts with ``register-python-argcomplete``::

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

Tcsh Support
------------
To activate completions for tcsh use::

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

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

    complete my-awesome-script '[email protected]*@`python-argcomplete-tcsh my-awesome-script`@'

Fish Support
------------
To activate completions for fish use::

    register-python-argcomplete --shell fish my-awesome-script | source

or create new completion file, e.g::

    register-python-argcomplete --shell fish my-awesome-script > ~/.config/fish/completions/my-awesome-script.fish

Completion Description For Fish

By default help string is added as completion description.

.. image:: docs/fish_help_string.png

You can disable this feature by removing _ARGCOMPLETE_DFS variable, e.g::

register-python-argcomplete --shell fish my-awesome-script | grep -v _ARGCOMPLETE_DFS | .

Git Bash Support

Due to limitations of file descriptor inheritance on Windows, Git Bash not supported out of the box. You can opt in to using temporary files instead of file descriptors for for IPC by setting the environment variable ARGCOMPLETE_USE_TEMPFILES, e.g. by adding export ARGCOMPLETE_USE_TEMPFILES=1 to ~/.bashrc.

For full support, consider using Bash with the Windows Subsystem for Linux (WSL).

External argcomplete script

To register an argcomplete script for an arbitrary name, the --external-argcomplete-script argument of the register-python-argcomplete script can be used::

eval "$(register-python-argcomplete --external-argcomplete-script /path/to/script arbitrary-name)"

This allows, for example, to use the auto completion functionality of argcomplete for an application not written in Python. The command line interface of this program must be additionally implemented in a Python script with argparse and argcomplete and whenever the application is called the registered external argcomplete script is used for auto completion.

This option can also be used in combination with the other supported shells.

Python Support

Argcomplete requires Python 2.7 or 3.5+.

Common Problems

If global completion is not completing your script, bash may have registered a default completion function::

$ complete | grep my-awesome-script
complete -F _minimal my-awesome-script

You can fix this by restarting your shell, or by running complete -r my-awesome-script.

Debugging

Set the _ARC_DEBUG variable in your shell to enable verbose debug output every time argcomplete runs. This will disrupt the command line composition state of your terminal, but make it possible to see the internal state of the completer if it encounters problems.

Acknowledgments

Inspired and informed by the optcomplete_ module by Martin Blais.

.. _optcomplete: http://pypi.python.org/pypi/optcomplete

Links

• Project home page (GitHub) <https://github.com/kislyuk/argcomplete>_
• Documentation <https://kislyuk.github.io/argcomplete/>_
• Package distribution (PyPI) <https://pypi.python.org/pypi/argcomplete>_
• Change log <https://github.com/kislyuk/argcomplete/blob/master/Changes.rst>_
• xontrib-argcomplete <https://github.com/anki-code/xontrib-argcomplete>_ - support argcomplete in xonsh <https://github.com/xonsh/xonsh>_ shell

Bugs

Please report bugs, issues, feature requests, etc. on `GitHub <https://github.com/kislyuk/argcomplete/issues>`_.

License
-------
Licensed under the terms of the `Apache License, Version 2.0 <http://www.apache.org/licenses/LICENSE-2.0>`_.

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