{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "nbsphinx": "hidden"
   },
   "source": [
    "This notebook is part of the `nbsphinx` documentation: https://nbsphinx.readthedocs.io/."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Configuring the Kernels"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Kernel Name\n",
    "\n",
    "If we have multiple kernels installed, we can choose to override the kernel saved in the notebook using [nbsphinx_kernel_name](usage.ipynb#nbsphinx_kernel_name):\n",
    "```python\n",
    "nbsphinx_kernel_name = 'python-upstream-dev'\n",
    "```\n",
    "which uses the kernel named `python-upstream-dev` instead of the kernel name stored in the notebook."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Kernel Arguments\n",
    "\n",
    "We can also pass options to the kernel by setting [nbsphinx_execute_arguments](usage.ipynb#nbsphinx_execute_arguments) in `conf.py`. These work the same way as `ipython_kernel_config.py`. For example, using\n",
    "```python\n",
    "nbsphinx_execute_arguments = [\n",
    "    \"--InlineBackend.rc=figure.dpi=96\",\n",
    "]\n",
    "```\n",
    "to set [plot options](code-cells.ipynb#Plots) is the same as writing:\n",
    "```python\n",
    "c.InlineBackend.rc = {'figure.dpi': 96}\n",
    "```\n",
    "in `ipython_kernel_config.py` or using:\n",
    "```ipython\n",
    "%config InlineBackend.rc={'figure.dpi': 96}\n",
    "```\n",
    "at the top of a notebook:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "get_ipython().config.InlineBackend.rc"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Environment Variables\n",
    "\n",
    "The contents of `os.environ` after the execution of `conf.py` will be passed as environment variables to the kernel. As an example, `MY_DUMMY_VARIABLE` has been set in [conf.py](conf.py) like this:\n",
    "\n",
    "```python\n",
    "import os\n",
    "os.environ['MY_DUMMY_VARIABLE'] = 'Hello from conf.py!'\n",
    "```\n",
    "\n",
    "... and it can be checked in the notebook like this:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import os\n",
    "os.environ['MY_DUMMY_VARIABLE']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is useful if we want to edit `PYTHONPATH` in order to compile the documentation without installing the project:\n",
    "```python\n",
    "import os\n",
    "\n",
    "src = os.path.abspath('../src')\n",
    "os.environ['PYTHONPATH'] = src\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If you are using https://mybinder.org/ and you want to define environment variables,\n",
    "you should create a file `.binder/start` in your repository\n",
    "(see [Binder docs](https://mybinder.readthedocs.io/en/latest/using/config_files.html#start-run-code-before-the-user-sessions-starts))\n",
    "containing definitions like this:\n",
    "\n",
    "```bash\n",
    "#!/bin/bash\n",
    "export MY_DUMMY_VARIABLE=\"Hello from .binder/start!\"\n",
    "exec \"$@\"\n",
    "```"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.7.6rc1"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}