Describing code in Sphinx¶
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.
Documenting Python objects¶
Sphinx offers several roles and directives to document Python objects,
all grouped together in the Python domain. For example,
you can use the
py:function directive to document a Python function,
Creating recipes ---------------- To retrieve a list of random ingredients, you can use the ``lumache.get_random_ingredients()`` function: .. py:function:: lumache.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 :return: The ingredients list. :rtype: list[str]
Which will render like this:
Notice several things:
Sphinx parsed the argument of the
.. py:functiondirective and highlighted the module, the function name, and the parameters appropriately.
The directive content includes a one-line description of the function, as well as a info field list containing the function parameter, its expected type, the return value, and the return type.
py: prefix specifies the domain. You may configure the
default domain so you can omit the prefix, either globally using the
primary_domain configuration, or use the
default-domain directive to change it from the point it is called
until the end of the file.
For example, if you set it to
py (the default), you can write
.. function:: directly.
Cross-referencing Python objects¶
By default, most of these directives generate entities that can be
cross-referenced from any part of the documentation by using
a corresponding role. For the case of functions,
you can use
py:func for that, as follows:
The ``kind`` parameter should be either ``"meat"``, ``"fish"``, or ``"veggies"``. Otherwise, :py:func:`lumache.get_random_ingredients` will raise an exception.
When generating code documentation, Sphinx will generate a cross-reference automatically just
by using the name of the object, without you having to explicitly use a role
for that. For example, you can describe the custom exception raised by the
function using the
.. py:exception:: lumache.InvalidKindError Raised if the kind is invalid.
Then, add this exception to the original description of the function:
.. py:function:: lumache.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]
And finally, this is how the result would look:
Beautiful, isn’t it?
Including doctests in your documentation¶
Since you are now describing code from a Python library, it will become useful to keep both the documentation and the code as synchronized as possible. One of the ways to do that in Sphinx is to include code snippets in the documentation, called doctests, that are executed when the documentation is built.
To demonstrate doctests and other Sphinx features covered in this tutorial,
Sphinx will need to be able to import the code. To achieve that, write this
at the beginning of
# If extensions (or modules to document with autodoc) are in another directory, # add these directories to sys.path here. import pathlib import sys sys.path.insert(0, pathlib.Path(__file__).parents.resolve().as_posix())
An alternative to changing the
sys.path variable is to create a
pyproject.toml file and make the code installable,
so it behaves like any other Python library. However, the
approach is simpler.
Then, before adding doctests to your documentation, enable the
doctest extension in
extensions = [ 'sphinx.ext.duration', 'sphinx.ext.doctest', ]
Next, write a doctest block as follows:
>>> import lumache >>> lumache.get_random_ingredients() ['shells', 'gorgonzola', 'parsley']
Doctests include the Python instructions to be run preceded by
the standard Python interpreter prompt, as well as the expected output
of each instruction. This way, Sphinx can check whether the actual output
matches the expected one.
To observe how a doctest failure looks like (rather than a code error as
above), let’s write the return value incorrectly first. Therefore, add a
get_random_ingredients like this:
def get_random_ingredients(kind=None): return ["eggs", "bacon", "spam"]
You can now run
make doctest to execute the doctests of your documentation.
Initially this will display an error, since the actual code does not behave
(.venv) $ make doctest Running Sphinx v4.2.0 loading pickled environment... done ... running tests... Document: usage --------------- ********************************************************************** File "usage.rst", line 44, in default Failed example: lumache.get_random_ingredients() Expected: ['shells', 'gorgonzola', 'parsley'] Got: ['eggs', 'bacon', 'spam'] ********************************************************************** ... make: *** [Makefile:20: doctest] Error 1
As you can see, doctest reports the expected and the actual results, for easy examination. It is now time to fix the function:
def get_random_ingredients(kind=None): return ["shells", "gorgonzola", "parsley"]
make test reports success!
For big projects though, this manual approach can become a bit tedious. In the next section, you will see how to automate the process.