Pre-installed packages#

xeus-python allows you to pre-install packages in the Python runtime. You can pre-install packages by adding an environment.yml file in the JupyterLite build directory, this file will be found automatically by xeus-python which will pre-build the environment when running jupyter lite build.

Furthermore, this automatically installs any labextension that it founds, for example installing ipyleaflet will make ipyleaflet work without the need to manually install the jupyter-leaflet labextension.

Say you want to install NumPy, Matplotlib and ipycanvas, it can be done by creating the environment.yml file with the following content:

name: xeus-python-kernel
- numpy
- matplotlib
- ipycanvas

Then you only need to build JupyterLite:

jupyter lite build

You can also pick another name for that environment file (e.g. custom.yml), by doing so, you will need to specify that name to xeus-python:

jupyter lite build --XeusPythonEnv.environment_file=custom.yml


It is common to provide pip dependencies in a conda environment file. This is currently not supported by xeus-python, but there is a work-in-progress to support it.

Then those packages are usable directly:

Try it!

Advanced Configuration#


This section is mostly for reference and should not be needed for regular use of the jupyterlite-xeus-python kernel.

Provide a custom empack_config.yaml#

Packages sometimes ship more data than needed for the package to work (tests, documentation, data files etc). This is fine on a regular installation of the package, but in the emscripten case when running in the browser this means that starting the kernel would download more files. For this reason, empack filters out anything that is not required for the Python code to run. It does it by following a set of filtering rules available in this file: emscripten-forge/empack.

But this default filtering could break some packages. In that case you would probably want to either contribute to the default empack config, or provide your own set of filtering rules.

The xeus-python kernel supports passing a custom empack_config.yaml. This file can be used to override the default filter rules set by the underlying empack tool used for packing the environment.

If you would like to provide additional rules for including or excluding files in the packed environment, create a empack_config.yaml with the following content as an example:

      - pattern: '**/*.py'
      - pattern: '**/static/css/*.css'
      - pattern: '**/static/html/*.html'

This example defines a set of custom rules for the xarray package to make sure it includes some static files that should be available from the kernel.

You can use this file when building JupyterLite:

jupyter lite build --XeusPythonEnv.empack_config=empack_config.yaml


Filtering files helps reduce the size of the assets to download and as a consequence reduce network traffic.