Tutorial: Extensions (Xontribs)¶
Take a deep breath and prepare for some serious Show & Tell; it’s time to learn about xonsh extensions!
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:
Structure¶
Xontribs are modules written in either xonsh (*.xsh
) or Python (*.py
).
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 cookiecutter with 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 config file,
dynamically at runtime with the xontrib
command, or by importing the
module normally. Since these extensions are just Python modules, by
default, they cannot be unloaded (easily).
Note
When a xontrib is loaded its public variables are placed in the current
execution context unless __all__
is defined, just like in regular Python
modules.
Extensions are loaded via the xontrib
command, which is a xonsh default
alias. This command may be run from anywhere in a xonshrc file or at any point
after xonsh has started up. Loading is the default action of the xontrib
command. Thus the following methods for loading via this command are equivalent:
xontrib myext mpl mypkg.show
xontrib load myext mpl mypkg.show
Loading the same xontrib multiple times does not have any effect after the first. Xontribs are simply Python modules, and therefore follow the same caching rules. So by the same token, you can also import them normally. Of course, you have to use the full module name to import a xontrib:
import xontrib.mpl
from xontrib import myext
from mypkg.show import *
Listing Known Xontribs¶
In addition to loading extensions, the xontrib
command also allows you to
list the known xontribs. This command will report whether known xontribs are
installed and if they are loaded in the current session. To display this
information, pass the list
action to the xontrib
command:
>>> xontrib list
mpl installed not-loaded
myext not-installed not-loaded
By default, this will display information for all known xontribs. However, you can restrict this to a set of names passed in on the command line.
>>> xontrib list mpl
mpl installed 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 this is a good idea, in general, because then:
- Your xontrib will show up as an extension the xonsh website,
- It will appear in the
xontrib list
command, and - It will show up in
xonfig wizard
.
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.
To register a xontrib, add an entry to
the xontribs.json file
in the main xonsh repository. A pull request is probably best, but if you
are having trouble figuring it out please contact one of the xonsh devs
with the relevant information.
This is a JSON file with two top-level keys: "xontribs"
and "packages"
.
The "xontribs"
key is a list of dictionaries that describes the xontrib
module itself. Such entries have the following structure:
{"xontribs": [
{"name": "xontrib-name",
"package": "package-name",
"url": "http://example.com/api/xontrib",
"description": ["Textual description as string or list or strings ",
"enabling long content to be split over many lines."]
}
]
}
The "packages"
key, on the other hand, is a dict mapping package names
(associated with the xontrib entries) to metadata about the package. Package
entries have the following structure:
{"packages": {
"package-name": {
"license": "WTFPL v1.1",
"url": "http://example",
"install": {
"conda": "conda install package-name",
"pip": "xpip install package-name"}
}
}
}
Note that you can have as many entries in the "install"
dict as you
want. Also, the keys are arbitrary labels, so feel free to pick whatever
you want.
Go forth!