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# Tutorial: Extensions (Xontribs)

Take a deep breath and prepare for some serious Show & Tell; it’s time to learn about xonsh extensions!

Xonsh comes with some default set of extensions. These can be viewed `here`.

Also checkout the list of Awesome Contributions from the community.

## Overview

Xontributions, or `xontribs`, are a set of tools and conventions for extending the functionality of xonsh beyond what is provided by default. This allows 3rd party developers and users to improve their xonsh experience without having to go through the xonsh development and release cycle.

Many tools and libraries have extension capabilities. Here are some that we took inspiration from for xonsh:

- Sphinx: Extensions are just Python modules, bundles some extensions with the main package, interface is a list of string names.

- IPython: Extensions are just Python modules with some special functions to load/unload.

- Oh My Zsh: Centralized registry, autoloading, and for a shell.

- ESLint: Ability to use language package manager to install/remove extensions.

## Structure

Xontribs are modules with some special functions written in either xonsh (`*.xsh`) or Python (`*.py`).

Here is a template:

    from xonsh.built_ins import XonshSession

    def _load_xontrib_(xsh: XonshSession, **kwargs) -> dict:
        """
        this function will be called when loading/reloading the xontrib.

        Args:
            xsh: the current xonsh session instance, serves as the interface to manipulate the session.
                 This allows you to register new aliases, history backends, event listeners ...
            **kwargs: it is empty as of now. Kept for future proofing.
        Returns:
            dict: this will get loaded into the current execution context
        """

    def _unload_xontrib_(xsh: XonshSession, **kwargs) -> dict:
        """If you want your extension to be unloadable, put that logic here"""

This _load_xontrib_() function is called after your extension is imported, and the currently active `xonsh.built_ins.XonshSession` instance is passed as the argument.

Note

Xontribs without `_load_xontrib_` are still supported. But when such xontrib is loaded, variables listed in `__all__` are placed in the current execution context if defined.

Normally, these are stored and found in an implicit namespace package called `xontrib`. However, xontribs may be placed in any package or directory that is on the `$PYTHONPATH`.

If a module is in the `xontrib` namespace package, it can be referred to just by its module name. If a module is in any other package, then it must be referred to by its full package path, separated by `.` like you would in an import statement. Of course, a module in `xontrib` may be referred to with the full `xontrib.myext`. But just calling it `myext` is a lot shorter and one of the main advantages of placing an extension in the `xontrib` namespace package.

Here is a sample file system layout and what the xontrib names would be:

    |- xontrib/
       |- javert.xsh     # "javert", because in xontrib
       |- your.py        # "your",
       |- eyes/
          |- __init__.py
          |- scream.xsh  # "eyes.scream", because eyes is in xontrib
    |- mypkg/
       |- __init__.py    # a regular package with an init file
       |- other.py       # not a xontrib
       |- show.py        # "mypkg.show", full module name
       |- tell.xsh       # "mypkg.tell", full module name
       |- subpkg/
          |- __init__.py
          |- done.py     # "mypkg.subpkg.done", full module name

You can also use the xontrib template to easily create the layout for your xontrib package.

## Loading Xontribs

Xontribs may be loaded in a few different ways: from the xonshrc file (e.g. `~/.xonshrc`), dynamically at runtime with the `xontrib` command, or its Python API.

Extensions are loaded via the `xontrib load` command. This command may be run from anywhere in a xonshrc file or at any point after xonsh has started up.

    xontrib load myext mpl mypkg.show

The same can be done in Python as well

    from xonsh.xontribs import xontribs_load
    xontribs_load(['myext', 'mpl', 'mypkg.show'])

A xontrib can be unloaded from the current session using `xontrib unload`

    xontrib unload myext mpl mypkg.show

Xontribs can use setuptools entrypoints to mark themselves available for autoloading using the below format.

    [options.entry_points]
    xonsh.xontribs =
        xontrib_name = path.to.the.module

Here the module should contain `_load_xontrib_` function as described above.

Note

Please make sure that importing the xontrib module and calling `_load_xontrib_` is fast enough. Otherwise it will affect the shell’s startup time. Any other imports or heavy computations should be done in lazy manner whenever possible.

## Listing Known Xontribs

In addition to loading extensions, the `xontrib` command also allows you to list the installed xontribs. This command will report if they are loaded in the current session. To display this information, pass the `list` action to the `xontrib` command:

    @ xontrib list
    mpl     not-loaded
    myext   not-loaded

For programmatic access, you may also have this command print a JSON formatted string:

    @ xontrib list --json mpl
    {"mpl": {"loaded": false, "installed": true}}

## Authoring Xontribs

Writing a xontrib is as easy as writing a xonsh or Python file and sticking it in a directory named `xontrib/`. However, please do not place an `__init__.py` in the `xontrib/` directory. It is an implicit namespace package and should not have one. See PEP 420 for more details.

Warning

Do not place an `__init__.py` in the `xontrib/` directory!

If you plan on using `*.xsh` files in you xontrib, then you’ll have to add some hooks to distutils, setuptools, pip, etc. to install these files. Try adding entries like the following entries to your `setup()` call in your `setup.py`:

    try:
        from setuptools import setup
    except ImportError:
        from distutils.core import setup

    setup(...,
          packages=[..., 'xontrib'],
          package_dir={..., 'xontrib': 'xontrib'},
          package_data={..., 'xontrib': ['*.xsh']},
          ...)

Something similar can be done for any non-xontrib package or sub-package that needs to distribute `*.xsh` files.

## Tell Us About Your Xontrib!

We request that you register your xontrib with us. We think that will make your contribution more discoverable.

To register a xontrib, create a `PullRequest` at Awesome-xontribs repository. Also, if you use Github to host your code, please add xonsh and xontrib to the topics.

All of this let’s users know that your xontrib is out there, ready to be used. Of course, you’re under no obligation to register your xontrib. Users will still be able to load your xontrib, as long as they have it installed.

Go forth!