Documenting Python Programs

Docstring conventions are described within PEP 257. Their purpose is to provide your users with a brief overview of the object. They should be kept concise enough to be easy to maintain but still be elaborate enough for new users to understand their purpose and how to use the documented object.

In all cases, the docstrings should use the triple-double quote (""") string format. This should be done whether the docstring is multi-lined or not. At a bare minimum, a docstring should be a quick summary of whatever is it you’re describing and should be contained within a single line.

Start with a capital letter, and end with a period.

From pep258, the docstring is a phrase ending in a period. It prescribes the function or method's effect as a command ("Do this", "Return that"), not as a description; e.g. don't write "Returns the pathname …".

def say_hello(name):
   '''
   Print message, returns nothing

   A simple function that demonstrates docstrings, - oh and also 
   says hello to the name passed to it.
   '''

   print(f"Hello {name}.  Try running help(say_hello) to see the docstring")

def say_hello(name):
   '''A simple function that demonstrates multi-line docstrings. 

   This is the elaboration of this function (or object).  It can be
   for a program itself (i.e. a module) or for a function within the
   module.   This particular case it is for a module that simply
   says hello to the name passed to it'''

   # first line of rest of the function
   print(f"Hello {name}.  Try typing 'help(say_hello)' to see the docstring")

From realpython :

There are specific docstrings formats that can be used to help docstring parsers and users have a familiar and known format. The formatting used within the examples in this tutorial are NumPy/SciPy-style docstrings.

You can choose the one of your liking, but stay consistent in a project.

Some of the most common formats are the following:

Formatting type	Description	Formal
		Specification
Google docstrings	Google's reommended	No
	form of documentation
reStructured Text	Official Python documentation
	standard. Feature rich, but	Yes
	not beginner friendly
NumPy/SciPy	NumPy's combination of
docstrings	reStructured and Google docstrings	Yes
Epytext	A Python adaption of Epydoc
	Great for Java developers	Yes

Example from NumPy/SciPy

"""Gets and prints the spreadsheet's header columns

Parameters
----------
file_loc : str
    The file location of the spreadsheet
print_cols : bool, optional
    A flag used to print the columns to the console (default is False)

Returns
-------
list
    a list of strings representing the header columns
"""

Here is another example:

class Vehicles(object):
  '''
  The Vehicles object contains lots of vehicles

  Parameters
  ----------
  arg : str
      The arg is used for ...
  *args
      The variable arguments are used for ...
  **kwargs
      The keyword arguments are used for ...

  Attributes
  ----------
  arg : str
      This is where we store arg,
  '''
  def __init__(self, arg, *args, **kwargs):
      self.arg = arg

  def cars(self, distance, destination):
      '''We can't travel distance in vehicles without fuels, so here is the fuels

      Parameters
      ----------
      distance : int
          The amount of distance traveled
      destination : bool
          Should the fuels refilled to cover the distance?

      Raises
      ------
      RuntimeError
          Out of fuel

      Returns
      -------
      cars
          A car mileage
      '''
      pass

Yet a third good example showing best practice to list each argument on a separate line.

def complex(real=0.0, imag=0.0):
    """Form a complex number.

    Keyword arguments:
    real -- the real part (default 0.0)
    imag -- the imaginary part (default 0.0)
    """
    if imag == 0.0 and real == 0.0:
        return complex_zero
    ...

Unless the entire docstring fits on a line, place the closing quotes on a line by themselves. This way, Emacs' fill-paragraph command can be used on it.

cm.py is a module (i.e. no hash-bang line to start) that has as its very first line, the doctring as follows:

'''Print examples using all the possible colours.

Use this to pick out the colour and text highlighting you want to use with your program, then copy the appropriate code to paste into your own print strings.

This program has no imports, and is merely an example of coloured outputs, as well as style outputs.

'''

etc etc.

After importing cm, import cm I ran help(cm) when I got this:

Help on module cm:

NAME
    cm - This utility prints examples using all the possible colours

DESCRIPTION
    Use this to pick out the colour and text highlighting you want
    to use with your program, then copy the appropriate code to
    paste into your own print strings.
    
    This program has no imports, and is merely an example of
    coloured outputs, as well as style outputs.

FILE
    /Users/zintis/bin/python/bin/cm.py

(END)

As you can see, it even gave me the full path of the module, without me having to manually specify it.

These "rules" were taken from ictshore.

Who said your docstrings should contain boring text? They shouldn’t! In fact, you should write them with the reStructured Text (RST) syntax.

RST is a way of writing text document so that they remain readable as text document, but can be parsed into something more graphical as well.

RST is a syntax for plain-text document that adds embellishments when processed with an RST reader. However, you can still read it as plain text.

RST Syntax for people in a hurry Python documentation heavily rely on RST. This doesn’t mean you have to know it all, but knowing some is certainly good. This is what you will be adding all the time in your docstrings.

text makes the text bold. text makes the text italic. You can combine the two above in text, which results in bold and italic. You can also add an underline to your text with =, * and - to make the text look like a title. Optionally, you can add also the same line above the text, the effect won’t change. However, the underline should be as long as the text, or even longer.

Heading ===== Subheading ** Even smaller heading

---

You can also use the special syntax :func: to reference a function (or method), :class: to reference a class and :mod: to reference a module. After that, write the component name between special quotes as in the example below. When a RST parser will build the text, it will create a link to the component you are referencing. Much better than writing just the component name.

:mod:`mymodule` :class:`mymodule.MyClass` :func:`mymodule.MyClass.my<sub>method</sub>` :func:`mymodule.my<sub>function</sub>` Sometimes, things can look really ugly if you have a long dependency tree like mysupermodule.mysubmodule.MyClass.my_method. Showing all of that is cumbersome, for no reason. We can avoid that with ~: adding this symbol at the beginning of the reference will show only the last item. For example, :func:`~mysupermodule.mysubmodule.MyClass.my<sub>method</sub>` will render simply as my_method. Of course, the link will still point to the correct position.

Multi-line docstrings consist of:

• summary line just like a one-line docstring, followed by
• a blank line, followed by
• a more elaborate description.

The summary line may be used by automatic indexing tools; it is important that it fits on one line and is separated from the rest of the docstring by a blank line. The summary line may be on the same line as the opening quotes or on the next line. The entire docstring is indented the same as the quotes at its first line (see example below).

Insert a blank line after all docstrings (one-line & multi-line) that document a class – generally speaking, the class's methods are separated from each other by a single blank line, and the docstring needs to be offset from the first method by a blank line.

The docstring of a script (a stand-alone program) should be usable as its "usage" message, printed when the script is invoked with incorrect or missing arguments (or perhaps with a "-h" option, for "help"). Such a docstring should document the script's function and command line syntax, environment variables, and files. Usage messages can be fairly elaborate (several screens full) and should be sufficient for a new user to use the command properly, as well as a complete quick reference to all options and arguments for the sophisticated user.

The docstring for a module should generally list the classes, exceptions and functions (and any other objects) that are exported by the module, with a one-line summary of each. (These summaries generally give less detail than the summary line in the object's docstring.) The docstring for a package (i.e., the docstring of the package's init.py module) should also list the modules and subpackages exported by the package.

The docstring for a function or method should summarize its behavior and document its arguments, return value(s), side effects, exceptions raised, and restrictions on when it can be called (all if applicable). Optional arguments should be indicated. It should be documented whether keyword arguments are part of the interface.

The docstring for a class should summarize its behavior and list the public methods and instance variables. If the class is intended to be subclassed, and has an additional interface for subclasses, this interface should be listed separately (in the docstring). The class constructor should be documented in the docstring for its init method. Individual methods should be documented by their own docstring.

If a class subclasses another class and its behavior is mostly inherited from that class, its docstring should mention this and summarize the differences. Use the verb "override" to indicate that a subclass method replaces a superclass method and does not call the superclass method; use the verb "extend" to indicate that a subclass method calls the superclass method (in addition to its own behavior).

Do not use the Emacs convention of mentioning the arguments of functions or methods in upper case in running text. Python is case sensitive and the argument names can be used for keyword arguments, so the docstring should document the correct argument names. It is best to list each argument on a separate line.

oding: utf-8 -*- """Example Google style docstrings.

This module demonstrates documentation as specified by the `Google Python Style Guide`_. Docstrings may extend over multiple lines. Sections are created with a section header and a colon followed by a block of indented text.

Example: Examples can be given using either the ``Example`` or ``Examples`` sections. Sections support any reStructuredText formatting, including literal blocks::

$ python example_google.py

Section breaks are created by resuming unindented text. Section breaks are also implicitly created anytime a new section starts.

Attributes: module_{levelvariable1} (int): Module level variables may be documented in either the ``Attributes`` section of the module docstring, or in an inline docstring immediately following the variable.

Either form is acceptable, but the two should not be mixed. Choose one convention to document module level variables and be consistent with it.

Todo:

• For module TODOs
• You have to also use ``sphinx.ext.todo`` extension

.. _Google Python Style Guide: http://google.github.io/styleguide/pyguide.html

"""

module_{levelvariable1} = 12345

module_{levelvariable2} = 98765 """int: Module level variable documented inline.

The docstring may span multiple lines. The type may optionally be specified on the first line, separated by a colon. """

def function_{withtypesindocstring}(param1, param2): """Example function with types documented in the docstring.

`PEP 484`_ type annotations are supported. If attribute, parameter, and return types are annotated according to `PEP 484`_, they do not need to be included in the docstring:

Args: param1 (int): The first parameter. param2 (str): The second parameter.

Returns: bool: The return value. True for success, False otherwise.

.. _PEP 484: https://www.python.org/dev/peps/pep-0484/

"""

def function_{withpep484typeannotations}(param1: int, param2: str) -> bool: """Example function with PEP 484 type annotations.

Args: param1: The first parameter. param2: The second parameter.

Returns: The return value. True for success, False otherwise.

"""

def module_{levelfunction}(param1, param2=None, *args, **kwargs): """This is an example of a module level function.

Function parameters should be documented in the ``Args`` section. The name of each parameter is required. The type and description of each parameter is optional, but should be included if not obvious.

If \*args or \*\*kwargs are accepted, they should be listed as ``*args`` and ``**kwargs``.

The format for a parameter is::

name (type): description The description may span multiple lines. Following lines should be indented. The "(type)" is optional.

Multiple paragraphs are supported in parameter descriptions.

Args: param1 (int): The first parameter. param2 (:obj:`str`, optional): The second parameter. Defaults to None. Second line of description should be indented. *args: Variable length argument list. **kwargs: Arbitrary keyword arguments.

Returns: bool: True if successful, False otherwise.

The return type is optional and may be specified at the beginning of the ``Returns`` section followed by a colon.

The ``Returns`` section may span multiple lines and paragraphs. Following lines should be indented to match the first line.

The ``Returns`` section supports any reStructuredText formatting, including literal blocks::

{ 'param1': param1, 'param2': param2 }

Raises: AttributeError: The ``Raises`` section is a list of all exceptions that are relevant to the interface. ValueError: If `param2` is equal to `param1`.

""" if param1 == param2: raise ValueError('param1 may not be equal to param2') return True

def example_generator(n): """Generators have a ``Yields`` section instead of a ``Returns`` section.

Args: n (int): The upper limit of the range to generate, from 0 to `n` - 1.

Yields: int: The next number in the range of 0 to `n` - 1.

Examples: Examples should be written in doctest format, and should illustrate how to use the function.

>>> print([i for i in example_generator(4)]) [0, 1, 2, 3]

""" for i in range(n): yield i

class ExampleError(Exception): """Exceptions are documented in the same way as classes.

The init method may be documented in either the class level docstring, or as a docstring on the init method itself.

Either form is acceptable, but the two should not be mixed. Choose one convention to document the init method and be consistent with it.

Note: Do not include the `self` parameter in the ``Args`` section.

Args: msg (str): Human readable string describing the exception. code (:obj:`int`, optional): Error code.

Attributes: msg (str): Human readable string describing the exception. code (int): Exception error code.

"""

def __init__{(self, msg, code)}: self.msg = msg self.code = code

class ExampleClass(object): """The summary line for a class docstring should fit on one line.

If the class has public attributes, they may be documented here in an ``Attributes`` section and follow the same formatting as a function's ``Args`` section. Alternatively, attributes may be documented inline with the attribute's declaration (see init method below).

Properties created with the ``@property`` decorator should be documented in the property's getter method.

Attributes: attr1 (str): Description of `attr1`. attr2 (:obj:`int`, optional): Description of `attr2`.

"""

def init__{(self, param1, param2, param3)}: """Example of docstring on the __init method.

The init method may be documented in either the class level docstring, or as a docstring on the init method itself.

Either form is acceptable, but the two should not be mixed. Choose one convention to document the init method and be consistent with it.

Note: Do not include the `self` parameter in the ``Args`` section.

Args: param1 (str): Description of `param1`. param2 (:obj:`int`, optional): Description of `param2`. Multiple lines are supported. param3 (:obj:`list` of :obj:`str`): Description of `param3`.

""" self.attr1 = param1 self.attr2 = param2 self.attr3 = param3 #: Doc comment inline with attribute

#: list of str: Doc comment before attribute, with type specified self.attr4 = ['attr4']

self.attr5 = None """str: Docstring after attribute, with type specified."""

@property def readonly_property(self): """str: Properties should be documented in their getter method.""" return 'readonly_property'

@property def readwrite_property(self): """:obj:`list` of :obj:`str`: Properties with both a getter and setter should only be documented in their getter method.

If the setter method contains notable behavior, it should be mentioned here. """ return ['readwrite_property']

@readwrite_{property.setter} def readwrite_property(self, value): value

def example_method(self, param1, param2): """Class methods are similar to regular functions.

Note: Do not include the `self` parameter in the ``Args`` section.

Args: param1: The first parameter. param2: The second parameter.

Returns: True if successful, False otherwise.

""" return True

def __special__(self): """By default special members with docstrings are not included.

Special members are any methods or attributes that start with and end with a double underscore. Any special member with a docstring will be included in the output, if ``napoleon<sub>includespecialwithdoc</sub>`` is set to True.

This behavior can be enabled by changing the following setting in Sphinx's conf.py::

napoleon_{includespecialwithdoc} = True

""" pass

def __{specialwithoutdocstring}__(self): pass

def _private(self): """By default private members are not included.

Private members are any methods or attributes that start with an underscore and are not special. By default they are not included in the output.

This behavior can be changed such that private members are included by changing the following setting in Sphinx's conf.py::

napoleon_{includeprivatewithdoc} = True

""" pass

def _private_{withoutdocstring}(self): pass