Add section on automatic documentation generation

doc/tutorial/automatic-doc-generation.rst

@@ -0,0 +1,88 @@
+Automatic documentation generation from code
+============================================
+
+In the :ref:`previous section <tutorial-describing-objects>` of the tutorial
+you manually documented a Python function in Sphinx. However, the description
+was out of sync with the code itself, since the function signature was not
+the same. Besides, it would be nice to reuse `Python
+docstrings <https://www.python.org/dev/peps/pep-0257/#what-is-a-docstring>`_
+in the documentation, rather than having to write the information in two
+places.
+
+Fortunately, :doc:`autodoc </usage/extensions/autodoc>` provides this
+functionality.
+
+Reusing signatures and docstrings with autodoc
+----------------------------------------------
+
+To use autodoc, first add it to the list of enabled extensions:
+
+.. code-block:: python
+   :caption: docs/source/conf.py
+   :emphasize-lines: 4
+
+   extensions = [
+       'sphinx.ext.duration',
+       'sphinx.ext.doctest',
+       'sphinx.ext.autodoc',
+   ]
+
+Next, move the content of the ``.. py:function`` directive to the function
+docstring in the original Python file and add an optional ``kind`` argument,
+as follows:
+
+.. code-block:: python
+   :caption: lumache.py
+   :emphasize-lines: 1-9
+
+   def get_random_ingredients(kind=None):
+       """
+       Return a list of random ingredients as strings.
+
+       :param kind: Optional "kind" of ingredients.
+       :type kind: list[str] or None
+       :raise lumache.InvalidKindError: If the kind is invalid.
+       :return: The ingredients list.
+       :rtype: list[str]
+
+       """
+       return ["shells", "gorgonzola", "parsley"]
+
+Finally, replace the ``.. py:function`` directive from the Sphinx documentation
+with :rst:dir:`autofunction`:
+
+.. code-block:: rst
+   :caption: docs/source/usage.rst
+   :emphasize-lines: 3
+
+   you can use the ``lumache.get_random_ingredients()`` function:
+
+   .. autofunction:: lumache.get_random_ingredients
+
+If you now build the HTML documentation, the output will be the same!
+Sphinx took the reStructuredText from the docstring and included it,
+also generating proper cross-references.
+
+You can also autogenerate documentation from other objects. For example, add
+the code for the ``InvalidKindError`` exception:
+
+.. code-block:: python
+   :caption: lumache.py
+
+   class InvalidKindError(Exception):
+       """Raised if the kind is invalid."""
+       pass
+
+And replace the ``.. py:exception`` directive with :rst:dir:`autoexception`
+as follows:
+
+.. code-block:: rst
+   :caption: docs/source/usage.rst
+   :emphasize-lines: 4
+
+   or ``"veggies"``. Otherwise, :py:func:`lumache.get_random_ingredients`
+   will raise an exception.
+
+   .. autoexception:: lumache.InvalidKindError
+
+And again, after running ``make html``, the output will be the same as before.

doc/tutorial/describing-code.rst

@@ -5,6 +5,8 @@ In the previous sections of the tutorial you can read how to write narrative
 or prose documentation in Sphinx. In this section you will describe code
 objects instead.
 
+.. _tutorial-describing-objects:
+
 Documenting Python objects
 --------------------------
 

doc/tutorial/index.rst

@@ -34,4 +34,5 @@ project.
    more-sphinx-customization
    narrative-documentation
    describing-code
+   automatic-doc-generation
    end