What is the correct way to document a **kwargs parameter?

Question

I\'m using sphinx and the autodoc plugin to generate API documentation for my Python modules. Whilst I can see how to nicely document specific parameters, I cannot find an exam

Answer 1

There is a doctstring example for Sphinx in their documentation. Specifically they show the following:

def public_fn_with_googley_docstring(name, state=None):
"""This function does something.

Args:
   name (str):  The name to use.

Kwargs:
   state (bool): Current state to be in.

Returns:
   int.  The return code::

      0 -- Success!
      1 -- No good.
      2 -- Try again.

Raises:
   AttributeError, KeyError

A really great idea.  A way you might use me is

>>> print public_fn_with_googley_docstring(name='foo', state=None)
0

BTW, this always returns 0.  **NEVER** use with :class:`MyPublicClass`.

"""
return 0

Though you asked about sphinx explicitly, I would also point to the Google Python Style Guide. Their docstring example seems to imply that they don't call out kwargs specifically. (other_silly_variable=None)

def fetch_bigtable_rows(big_table, keys, other_silly_variable=None):
"""Fetches rows from a Bigtable.

Retrieves rows pertaining to the given keys from the Table instance
represented by big_table.  Silly things may happen if
other_silly_variable is not None.

Args:
    big_table: An open Bigtable Table instance.
    keys: A sequence of strings representing the key of each table row
        to fetch.
    other_silly_variable: Another optional variable, that has a much
        longer name than the other args, and which does nothing.

Returns:
    A dict mapping keys to the corresponding table row data
    fetched. Each row is represented as a tuple of strings. For
    example:

    {'Serak': ('Rigel VII', 'Preparer'),
     'Zim': ('Irk', 'Invader'),
     'Lrrr': ('Omicron Persei 8', 'Emperor')}

    If a key from the keys argument is missing from the dictionary,
    then that row was not found in the table.

Raises:
    IOError: An error occurred accessing the bigtable.Table object.
"""
pass

A-B-B has a question about the accepted answer of referencing the subprocess management documentation. If you import a module, you can quickly see the module docstrings via inspect.getsource.

An example from the python interpreter using Silent Ghost's recommendation:

>>> import subprocess
>>> import inspect
>>> import print inspect.getsource(subprocess)

Of course you can also view the module documentation via help function. For example help(subprocess)

I'm not personally a fan of the subprocess docstring for kwargs as an example, but like the Google example it doesn't list kwargs seperately as shown in the Sphinx documentation example.

def call(*popenargs, **kwargs):
"""Run command with arguments.  Wait for command to complete, then
return the returncode attribute.

The arguments are the same as for the Popen constructor.  Example:

retcode = call(["ls", "-l"])
"""
return Popen(*popenargs, **kwargs).wait()

I'm including this answer to A-B-B's question because it's worth noting that you can review any module's source or documentation this way for insights and inspiration for commenting your code.

Answer 2

After finding this question I settled on the following, which is valid Sphinx and works fairly well:

def some_function(first, second="two", **kwargs):
    r"""Fetches and returns this thing

    :param first:
        The first parameter
    :type first: ``int``
    :param second:
        The second parameter
    :type second: ``str``
    :param \**kwargs:
        See below

    :Keyword Arguments:
        * *extra* (``list``) --
          Extra stuff
        * *supplement* (``dict``) --
          Additional content

    """

The r"""...""" is required to make this a "raw" docstring and thus keep the \* intact (for Sphinx to pick up as a literal * and not the start of "emphasis").

The chosen formatting (bulleted list with parenthesized type and m-dash-separated description) is simply to match the automated formatting provided by Sphinx.

Once you've gone to this effort of making the "Keyword Arguments" section look like the default "Parameters" section, it seems like it might be easier to roll your own parameters section from the outset (as per some of the other answers), but as a proof of concept this is one way to achieve a nice look for supplementary **kwargs if you're already using Sphinx.