.. _configuration:

Configuration
=============

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:

.. code::

    name: xeus-python-kernel
    channels:
    - https://repo.mamba.pm/emscripten-forge
    - https://repo.mamba.pm/conda-forge
    dependencies:
    - numpy
    - matplotlib
    - ipycanvas

Then you only need to build JupyterLite:

.. code::

    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:

.. code::

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

.. note::
    It is common to provide `pip` dependencies in a conda environment file, this is currently **not supported** by xeus-python.

Then those packages are usable directly:

.. replite::
   :kernel: xeus-python
   :height: 600px
   :prompt: Try it!

   %matplotlib inline

   import matplotlib.pyplot as plt
   import numpy as np

   fig = plt.figure()
   plt.plot(np.sin(np.linspace(0, 20, 100)))
   plt.show();