.. _documenting-matplotlib:

=====================
Writing documentation
=====================

.. contents:: Contents
   :depth: 2
   :local:
   :backlinks: top
   :class: multicol-toc


Getting started
===============


General file structure
----------------------

All documentation is built from the :file:`doc/` directory.  This directory
contains both reStructuredText (ReST_; ``.rst``) files that contain pages in
the documentation and configuration files for Sphinx_.

The ``.rst`` files are kept in :file:`doc/users`,
:file:`doc/devel`, :file:`doc/api` and :file:`doc/faq`. The main entry point is
:file:`doc/index.rst`, which pulls in the :file:`index.rst` file for the users
guide, developers guide, api reference, and FAQs. The documentation suite is
built as a single document in order to make the most effective use of cross
referencing.

Sphinx_ also creates ``.rst`` files that are staged in :file:`doc/api` from
the docstrings of the classes in the Matplotlib library.  Except for
:file:`doc/api/api_changes/`, these ``.rst`` files are created when the
documentation is built.

Similarly, the contents of :file:`docs/gallery` and :file:`docs/tutorials` are
generated by the `Sphinx Gallery`_ from the sources in :file:`examples` and
:file:`tutorials`.  These sources consist of python scripts that have ReST_
documentation built into their comments.  Don't directly edit the
``.rst`` files in :file:`docs/gallery` and :file:`docs/tutorials` as they are
regenerated when the documentation are built.

Installing dependencies
-----------------------

The documentation for Matplotlib is generated from reStructuredText (ReST_)
using the Sphinx_ documentation generation tool. There are several extra
requirements that are needed to build the documentation. They are listed in
:file:`doc-requirements.txt` and listed below:

* Sphinx>=1.3, !=1.5.0, !=1.6.4
* colorspacious
* IPython
* mock
* numpydoc>=0.4
* Pillow
* sphinx-gallery>=0.1.12
* graphviz

.. note::

  * You'll need a minimal working LaTeX distribution for many examples to run.
  * `Graphviz <http://www.graphviz.org/Download.php>`_ is not a Python package,
    and needs to be installed separately.

Building the docs
-----------------

The documentation sources are found in the :file:`doc/` directory in the trunk.
The configuration file for Sphinx is :file:`doc/conf.py`. It controls which
directories Sphinx parses, how the docs are built, and how the extensions are
used. To build the documentation in html format, cd into :file:`doc/` and run:

.. code-block:: sh

   make html

Other useful invocations include

.. code-block:: sh

   # Delete built files.  May help if you get errors about missing paths or
   # broken links.
   make clean

   # Build pdf docs.
   make latexpdf

The ``SPHINXOPTS`` variable is set to ``-W`` by default to turn warnings into
errors.  To unset it, use

.. code-block:: sh

   make SPHINXOPTS= html

You can use the ``O`` variable to set additional options:

* ``make O=-j4 html`` runs a parallel build with 4 processes.
* ``make O=-Dplot_formats=png:100 html`` saves figures in low resolution.
* ``make O=-Dplot_gallery=0 html`` skips the gallery build.

Multiple options can be combined using e.g. ``make O='-j4 -Dplot_gallery=0'
html``.

On Windows, options needs to be set as environment variables, e.g. ``set O=-W
-j4 & make html``.

.. _writing-rest-pages:

Writing ReST pages
==================

Most documentation is either in the docstring of individual
classes and methods, in explicit ``.rst`` files, or in examples and tutorials.
All of these use the ReST_ syntax. Users should look at the ReST_ documentation
for a full description. But some specific hints and conventions Matplotlib
uses are useful for creating documentation.

Formatting and style conventions
--------------------------------

It is useful to strive for consistency in the Matplotlib documentation.  Here
are some formatting and style conventions that are used.

Section name formatting
~~~~~~~~~~~~~~~~~~~~~~~

For everything but top-level chapters,  use ``Upper lower`` for
section titles, e.g., ``Possible hangups`` rather than ``Possible
Hangups``

Function arguments
~~~~~~~~~~~~~~~~~~

Function arguments and keywords within docstrings should be referred to using
the ``*emphasis*`` role. This will keep Matplotlib's documentation consistent
with Python's documentation:

.. code-block:: rst

  Here is a description of *argument*

Do not use the ```default role```:

.. code-block:: rst

   Do not describe `argument` like this.  As per the next section,
   this syntax will (unsuccessfully) attempt to resolve the argument as a
   link to a class or method in the library.

nor the ````literal```` role:

.. code-block:: rst

   Do not describe ``argument`` like this.


.. _internal-section-refs:

Referring to other documents and sections
-----------------------------------------

Sphinx_ allows internal references_ between documents.

Documents can be linked with the `:doc:` directive:

.. code-block:: rst

   See the :doc:`/faq/installing_faq`

   See the tutorial :doc:`/tutorials/introductory/sample_plots`

   See the example :doc:`/gallery/lines_bars_and_markers/simple_plot`

will render as:

  See the :doc:`/faq/installing_faq`

  See the tutorial :doc:`/tutorials/introductory/sample_plots`

  See the example :doc:`/gallery/lines_bars_and_markers/simple_plot`

Sections can also be given reference names.  For instance from the
:doc:`/faq/installing_faq` link:

.. code-block:: rst

   .. _clean-install:

   How to completely remove Matplotlib
   ===================================

   Occasionally, problems with Matplotlib can be solved with a clean...

and refer to it using the standard reference syntax:

.. code-block:: rst

   See :ref:`clean-install`

will give the following link: :ref:`clean-install`

To maximize internal consistency in section labeling and references,
use hyphen separated, descriptive labels for section references.
Keep in mind that contents may be reorganized later, so
avoid top level names in references like ``user`` or ``devel``
or ``faq`` unless necessary, because for example the FAQ "what is a
backend?" could later become part of the users guide, so the label:

.. code-block:: rst

   .. _what-is-a-backend:

is better than:

.. code-block:: rst

   .. _faq-backend:

In addition, since underscores are widely used by Sphinx itself, use
hyphens to separate words.

.. _referring-to-other-code:

Referring to other code
-----------------------

To link to other methods, classes, or modules in Matplotlib you can use
back ticks, for example:

.. code-block:: rst

  `matplotlib.collections.LineCollection`

generates a link like this: `matplotlib.collections.LineCollection`.

*Note:* We use the sphinx setting ``default_role = 'obj'`` so that you don't
have to use qualifiers like ``:class:``, ``:func:``, ``:meth:`` and the likes.

Often, you don't want to show the full package and module name. As long as the
target is unanbigous you can simply leave them out:

.. code-block:: rst

  `.LineCollection`

and the link still works: `.LineCollection`.

If there are multiple code elements with the same name (e.g. ``plot()`` is a
method in multiple classes), you'll have to extend the definition:

.. code-block:: rst

  `.pyplot.plot` or `.Axes.plot`

These will show up as `.pyplot.plot` or `.Axes.plot`. To still show only the
last segment you can add a tilde as prefix:

.. code-block:: rst

  `~.pyplot.plot` or `~.Axes.plot`

will render as `~.pyplot.plot` or `~.Axes.plot`.

Other packages can also be linked via
`intersphinx <http://www.sphinx-doc.org/en/master/ext/intersphinx.html>`_:

.. code-block:: rst

  `numpy.mean`

will return this link: `numpy.mean`.  This works for Python, Numpy, Scipy,
and Pandas (full list is in :file:`doc/conf.py`). Sometimes it is tricky
to get external Sphinx linking to work; to
check that a something exists to link to the following shell command outputs
a list of all objects that can be referenced (in this case for Numpy)::

  python -m sphinx.ext.intersphinx 'https://docs.scipy.org/doc/numpy/objects.inv'

.. _rst-figures-and-includes:

Including figures and files
---------------------------

Image files can directly included in pages with the ``image::`` directive.
e.g., :file:`users/navigation_toolbar.rst` displays the toolbar icons
with a call to a static image::

    .. image:: ../_static/toolbar.png

as rendered on the page: :ref:`navigation-toolbar`.

Files can be included verbatim.  For instance the ``matplotlibrc`` file
is important for customizing Matplotlib, and is included verbatim in the
tutorial in :doc:`/tutorials/introductory/customizing`::

    .. literalinclude:: ../../_static/matplotlibrc

This is rendered at the bottom of :doc:`/tutorials/introductory/customizing`.
Note that this is in a tutorial; see :ref:`writing-examples-and-tutorials`
below.

The examples directory is also copied to :file:`doc/gallery` by sphinx-gallery,
so plots from the examples directory can be included using

.. code-block:: rst

    .. plot:: gallery/pylab_examples/simple_plot.py

Note that the python script that generates the plot is referred to, rather than
any plot that is created.  Sphinx-gallery will provide the correct reference
when the documentation is built.


.. _writing-docstrings:

Writing docstrings
==================

Most of the API documentation is written in docstrings. These are comment
blocks in source code that explain how the code works.

.. note::

   Some parts of the documentation do not yet conform to the current
   documentation style. If in doubt, follow the rules given here and not what
   you may see in the source code. Pull requests updating docstrings to
   the current style are very welcome.

All new or edited docstrings should conform to the `numpydoc docstring guide`_.
Much of the ReST_ syntax discussed above (:ref:`writing-rest-pages`) can be
used for links and references.  These docstrings eventually populate the
:file:`doc/api` directory and form the reference documentation for the
library.

Example docstring
-----------------

An example docstring looks like:

.. code-block:: python

    def hlines(self, y, xmin, xmax, colors='k', linestyles='solid',
               label='', **kwargs):
        """
        Plot horizontal lines at each *y* from *xmin* to *xmax*.

        Parameters
        ----------
        y : float or array-like
            y-indexes where to plot the lines.

        xmin, xmax : float or array-like
            Respective beginning and end of each line. If scalars are
            provided, all lines will have the same length.

        colors : array-like of colors, optional, default: 'k'

        linestyles : {'solid', 'dashed', 'dashdot', 'dotted'}, optional

        label : string, optional, default: ''

        Returns
        -------
        lines : `~matplotlib.collections.LineCollection`

        Other Parameters
        ----------------
        **kwargs : `~matplotlib.collections.LineCollection` properties.

        See also
        --------
        vlines : vertical lines
        axhline: horizontal line across the axes
        """

See the `~.Axes.hlines` documentation for how this renders.

The Sphinx_ website also contains plenty of documentation_ concerning ReST
markup and working with Sphinx in general.

Formatting conventions
----------------------

The basic docstring conventions are covered in the `numpydoc docstring guide`_
and the Sphinx_ documentation.  Some Matplotlib-specific formatting conventions
to keep in mind:

Function arguments
   Function arguments and keywords within docstrings should be referred to
   using the ``*emphasis*`` role. This will keep Matplotlib's documentation
   consistent with Python's documentation:

   .. code-block:: rst

      If *linestyles* is *None*, the 'solid' is used.

   Do not use the ```default role``` or the ````literal```` role:

   .. code-block:: rst

      Neither `argument` nor ``argument`` should be used.


Quotes for strings
   Matplotlib does not have a convention whether to use single-quotes or
   double-quotes.  There is a mixture of both in the current code.

   Use simple single or double quotes when giving string values, e.g.:: rst

   .. code-block:: rst

      If 'tight', try to figure out the tight bbox of the figure.

Parameter type descriptions
   The main goal for parameter type descriptions is to be readable and
   understandable by humans. If the possible types are too complex use a
   simplification for the type description and explain the type more
   precisely in the text.

   Generally, the `numpydoc docstring guide`_ conventions apply. The following
   rules expand on them where the numpydoc conventions are not specific.

   Use ``float`` for a type that can be any number.

   Use ``array-like`` for homogeneous numeric sequences, which could
   typically be a numpy.array. Dimensionality may be specified using ``2D``,
   ``3D``, ``n-dimensional``. If you need to have variables denoting the
   sizes of the dimensions, use capital letters in brackets
   (``array-like (M, N)``). When refering to them in the text they are easier
   read and no special formatting is needed.

   ``float`` is the implicit default dtype for array-likes. For other dtypes
   use ``array-like of int``.

   Some possible uses::

      2D array-like
      array-like (N)
      array-like (M, N)
      array-like (M, N, 3)
      array-like of int

   Non-numeric homogeneous sequences are described as lists, e.g.::

      list of str
      list of `.Artist`

Referencing types
   Generally, the rules from referring-to-other-code_ apply. More specifically:

   Use full references ```~matplotlib.colors.Normalize``` with an
   abbreviation tilde in parameter types. While the full name helps the
   reader of plain text docstrings, the HTML does not need to show the full
   name as it links to it. Hence, the ``~``-shortening keeps it more readable.

   Use abbreviated links ```.Normalize``` in the text.

   .. code-block:: rst

      norm : `~matplotlib.colors.Normalize`, optional
         A `.Normalize` instance is used to scale luminance data to 0, 1.

``See also`` sections
   Sphinx automatically links code elements in the definition blocks of ``See
   also`` sections. No need to use backticks there::

       See also
       --------
       vlines : vertical lines
       axhline: horizontal line across the axes

Wrapping parameter lists
   Long parameter lists should be wrapped using a ``\`` for continuation and
   starting on the new line without any indent:

   .. code-block:: python

      def add_axes(self, *args, **kwargs):
          """
          ...

          Parameters
          ----------
          projection :
              {'aitoff', 'hammer', 'lambert', 'mollweide', 'polar', \
      'rectilinear'}, optional
              The projection type of the axes.

          ...
          """

   Alternatively, you can describe the valid parameter values in a dedicated
   section of the docstring.

rcParams
   rcParams can be referenced with the custom ``:rc:`` role:
   :literal:`:rc:\`foo\`` yields ``rcParams["foo"]``. Use `= [default-val]`
   to indicate the default value of the parameter. The default value should be
   literal, i.e. enclosed in double backticks. For simplicity these may be
   omitted for string default values.

   .. code-block:: rst

      If not provided, defaults to :rc:`figure.figsize` = ``[6.4, 4.8]``.
      If not provided, defaults to :rc:`figure.facecolor` = 'w'.

Deprecated formatting conventions
---------------------------------
Formerly, we have used square brackets for explicit parameter lists
``['solid' | 'dashed' | 'dotted']``. With numpydoc we have switched to their
standard using curly braces ``{'solid', 'dashed', 'dotted'}``.

Setters and getters
-------------------

Artist properties are implemented using setter and getter methods (because
Matplotlib predates the introductions of the `property` decorator in Python).
By convention, these setters and getters are named ``set_PROPERTYNAME`` and
``get_PROPERTYNAME``; the list of properties thusly defined on an artist and
their values can be listed by the `~.pyplot.setp` and `~.pyplot.getp` functions.

.. note::

   ``ACCEPTS`` blocks have recently become optional. You may now use a
   numpydoc ``Parameters`` block because the accepted values can now be read
   from the type description of the first parameter.

Property setter methods should indicate the values they accept using a (legacy)
special block in the docstring, starting with ``ACCEPTS``, as follows:

.. code-block:: python

   # in lines.py
   def set_linestyle(self, linestyle):
       """
       Set the linestyle of the line

       ACCEPTS: [ '-' | '--' | '-.' | ':' | 'steps' | 'None' | ' ' | '' ]
       """

The ACCEPTS block is used to render a table of all properties and their
acceptable values in the docs; it can also be displayed using, e.g.,
``plt.setp(Line2D)`` (all properties) or ``plt.setp(Line2D, 'linestyle')``
(just one property).

There are cases in which the ACCEPTS string is not useful in the
generated Sphinx documentation, e.g. if the valid parameters are already
defined in the numpydoc parameter list. You can hide the ACCEPTS string from
Sphinx by making it a ReST comment (i.e. use ``.. ACCEPTS:``):

.. code-block:: python

   def set_linestyle(self, linestyle):
       """
       An ACCEPTS string invisible to Sphinx.

       .. ACCEPTS: [ '-' | '--' | '-.' | ':' | 'steps' | 'None' | ' ' | '' ]
       """


Keyword arguments
-----------------

.. note::

  The information in this section is being actively discussed by the
  development team, so use the docstring interpolation only if necessary.
  This section has been left in place for now because this interpolation
  is part of the existing documentation.

Since Matplotlib uses a lot of pass-through ``kwargs``, e.g., in every function
that creates a line (`~.pyplot.plot`, `~.pyplot.semilogx`, `~.pyplot.semilogy`,
etc...), it can be difficult for the new user to know which ``kwargs`` are
supported.  Matplotlib uses a docstring interpolation scheme to support
documentation of every function that takes a ``**kwargs``.  The requirements
are:

1. single point of configuration so changes to the properties don't
   require multiple docstring edits.

2. as automated as possible so that as properties change, the docs
   are updated automatically.

The function `matplotlib.artist.kwdoc` and the decorator
`matplotlib.docstring.dedent_interpd` facilitate this.  They combine Python
string interpolation in the docstring with the Matplotlib artist introspection
facility that underlies ``setp`` and ``getp``.  The ``kwdoc`` function gives
the list of properties as a docstring. In order to use this in another
docstring, first update the ``matplotlib.docstring.interpd`` object, as seen in
this example from `matplotlib.lines`:

.. code-block:: python

  # in lines.py
  docstring.interpd.update(Line2D=artist.kwdoc(Line2D))

Then in any function accepting `~.Line2D` pass-through ``kwargs``, e.g.,
`matplotlib.axes.Axes.plot`:

.. code-block:: python

  # in axes.py
  @docstring.dedent_interpd
  def plot(self, *args, **kwargs):
      """
      Some stuff omitted

      The kwargs are Line2D properties:
      %(Line2D)s

      kwargs scalex and scaley, if defined, are passed on
      to autoscale_view to determine whether the x and y axes are
      autoscaled; default True.  See Axes.autoscale_view for more
      information
      """

Note there is a problem for `~matplotlib.artist.Artist` ``__init__`` methods,
e.g., `matplotlib.patches.Patch.__init__`, which supports ``Patch`` ``kwargs``,
since the artist inspector cannot work until the class is fully defined and
we can't modify the ``Patch.__init__.__doc__`` docstring outside the class
definition.  There are some some manual hacks in this case, violating the
"single entry point" requirement above -- see the ``docstring.interpd.update``
calls in `matplotlib.patches`.

.. _docstring-adding-figures:

Adding figures
--------------

As above (see :ref:`rst-figures-and-includes`), figures in the examples gallery
can be referenced with a `:plot:` directive pointing to the python script that
created the figure.  For instance the `~.Axes.legend` docstring references
the file :file:`examples/api/legend.py`:

.. code-block:: python

    """
     ...

    Examples
    --------

    .. plot:: gallery/api/legend.py
    """

Note that ``examples/api/legend.py`` has been mapped to
``gallery/api/legend.py``, a redirection that may be fixed in future
re-organization of the docs.

Plots can also be directly placed inside docstrings.  Details are in
:doc:`/devel/plot_directive`.  A short example is:

.. code-block:: python

    """
     ...

    Examples
    --------

    .. plot::
       import matplotlib.image as mpimg
       img = mpimg.imread('_static/stinkbug.png')
       imgplot = plt.imshow(img)
    """

An advantage of this style over referencing an example script is that the
code will also appear in interactive docstrings.

.. _writing-examples-and-tutorials:

Writing examples and tutorials
==============================

Examples and tutorials are python scripts that are run by `Sphinx Gallery`_
to create a gallery of images in the :file:`/doc/gallery` and
:file:`/doc/tutorials` directories respectively.  To exclude an example
from having an plot generated insert "sgskip" somewhere in the filename.

The format of these files is relatively straightforward.  Properly
formatted comment blocks are treated as ReST_ text, the code is
displayed, and figures are put into the built page.

For instance the example :doc:`/gallery/lines_bars_and_markers/simple_plot`
example is generated from
:file:`/examples/lines_bars_and_markers/simple_plot.py`, which looks like:

.. code-block:: python

    """
    ===========
    Simple Plot
    ===========

    Create a simple plot.
    """
    import matplotlib.pyplot as plt
    import numpy as np

    # Data for plotting
    t = np.arange(0.0, 2.0, 0.01)
    s = 1 + np.sin(2 * np.pi * t)

    # Note that using plt.subplots below is equivalent to using
    # fig = plt.figure and then ax = fig.add_subplot(111)
    fig, ax = plt.subplots()
    ax.plot(t, s)

    ax.set(xlabel='time (s)', ylabel='voltage (mV)',
           title='About as simple as it gets, folks')
    ax.grid()
    plt.show()

The first comment block is treated as ReST_ text.  The other comment blocks
render as comments in :doc:`/gallery/lines_bars_and_markers/simple_plot`.

Tutorials are made with the exact same mechanism, except they are longer, and
typically have more than one comment block (i.e.
:doc:`/tutorials/introductory/usage`).  The first comment block
can be the same as the example above.  Subsequent blocks of ReST text
are delimited by a line of `###` characters:

.. code-block:: python

    """
    ===========
    Simple Plot
    ===========

    Create a simple plot.
    """
    ...
    ax.grid()
    plt.show()

    ##########################################################################
    # Second plot
    # ===========
    #
    # This is a second plot that is very nice

    fig, ax = plt.subplots()
    ax.plot(np.sin(range(50)))

In this way text, code, and figures are output in a "notebook" style.

Miscellaneous
=============

Adding animations
-----------------

There is a Matplotlib Google/Gmail account with username ``mplgithub``
which was used to setup the github account but can be used for other
purposes, like hosting Google docs or Youtube videos.  You can embed a
Matplotlib animation in the docs by first saving the animation as a
movie using :meth:`matplotlib.animation.Animation.save`, and then
uploading to `matplotlib's Youtube
channel <https://www.youtube.com/user/matplotlib>`_ and inserting the
embedding string youtube provides like:

.. code-block:: rst

  .. raw:: html

     <iframe width="420" height="315"
       src="http://www.youtube.com/embed/32cjc6V0OZY"
       frameborder="0" allowfullscreen>
     </iframe>

An example save command to generate a movie looks like this

.. code-block:: python

    ani = animation.FuncAnimation(fig, animate, np.arange(1, len(y)),
        interval=25, blit=True, init_func=init)

    ani.save('double_pendulum.mp4', fps=15)

Contact Michael Droettboom for the login password to upload youtube videos of
google docs to the mplgithub account.

.. _inheritance-diagrams:

Generating inheritance diagrams
-------------------------------

Class inheritance diagrams can be generated with the
``inheritance-diagram`` directive.  To use it, provide the
directive with a number of class or module names (separated by
whitespace).  If a module name is provided, all classes in that module
will be used.  All of the ancestors of these classes will be included
in the inheritance diagram.

A single option is available: *parts* controls how many of parts in
the path to the class are shown.  For example, if *parts* == 1, the
class ``matplotlib.patches.Patch`` is shown as ``Patch``.  If *parts*
== 2, it is shown as ``patches.Patch``.  If *parts* == 0, the full
path is shown.

Example:

.. code-block:: rst

    .. inheritance-diagram:: matplotlib.patches matplotlib.lines matplotlib.text
       :parts: 2

.. inheritance-diagram:: matplotlib.patches matplotlib.lines matplotlib.text
   :parts: 2

.. _emacs-helpers:

Emacs helpers
-------------

There is an emacs mode `rst.el
<http://docutils.sourceforge.net/tools/editors/emacs/rst.el>`_ which
automates many important ReST tasks like building and updating
table-of-contents, and promoting or demoting section headings.  Here
is the basic ``.emacs`` configuration:

.. code-block:: lisp

    (require 'rst)
    (setq auto-mode-alist
          (append '(("\\.txt$" . rst-mode)
                    ("\\.rst$" . rst-mode)
                    ("\\.rest$" . rst-mode)) auto-mode-alist))

Some helpful functions::

    C-c TAB - rst-toc-insert

      Insert table of contents at point

    C-c C-u - rst-toc-update

        Update the table of contents at point

    C-c C-l rst-shift-region-left

        Shift region to the left

    C-c C-r rst-shift-region-right

        Shift region to the right

.. TODO: Add section about uploading docs

.. _ReST: http://docutils.sourceforge.net/rst.html
.. _Sphinx: http://www.sphinx-doc.org
.. _documentation: http://www.sphinx-doc.org/contents.html
.. _`inline markup`: http://www.sphinx-doc.org/markup/inline.html
.. _index: http://www.sphinx-doc.org/markup/para.html#index-generating-markup
.. _`Sphinx Gallery`: https://sphinx-gallery.readthedocs.io/en/latest/
.. _references: http://www.sphinx-doc.org/en/stable/markup/inline.html
.. _`numpydoc docstring guide`: https://numpydoc.readthedocs.io/en/latest/format.html
