Developer's guide
#################

:Author: Ben Finney <ben+python@benfinney.id.au>
:Updated: 2022-02-18


VCS repository
==============

The official Version Control System (VCS) for this code base is the
Git repository at `the ‘python-daemon’ Pagure project`_.

You can submit your proposed changes as merge requests:

* Use your Pagure account and use the “pull request” feature.

* Subscribe to `the ‘python-daemon-devel’ discussion forum`_ and
  direct us to a branch in your published fork.


..  _the ‘python-daemon’ Pagure project: https://pagure.io/python-daemon/
..  _the ‘python-daemon-devel’ discussion forum:
    https://lists.alioth.debian.org/mailman/listinfo/python-daemon-devel


Project layout
==============

::

    ./                  Top level of source tree
        doc/            Project documentation
        bin/            Executable programs
        daemon/         Main ‘daemon’ library
        test/           Unit tests


Code style
==========

Python
------

All Python code should conform to the guidelines in :PEP:`8` and :PEP:`257`.
In particular:

Indentation
+++++++++++

* Indent each level using 4 space characters (``U+0020 SPACE``).

* Indent continuation lines two levels (8 spaces). This will help
  distinguish them from adjacent code blocks indented one level.

  Do not attempt to align continuation lines with characters on the
  previous line.

* Do not insert TAB (``U+0008 CHARACTER TABULATION``) characters into
  source code. This allows the code to render the same in different
  programs, and improves the ability to cut-and-paste the code.

Example::

    flim = flambake(
            foo=eeny.meeny.miney.moe.Catcher(),
            bar="eggs", baz="spam")
    found_anomolous_wibble = False
    for wibble in flim:
        if wibble in [
                zork for zork in zorkulate(wibble)]:
            found_anomolous_wibble = True
            break
        wibble_accumulator.append(wibble)
    zinkify(wibble_accumulator)

Naming
++++++

* Name modules in lower case, ``multiplewordslikethis``.

* Name classes in title case, ``MultipleWordsLikeThis``.

* Name functions, instances, and other variables in lower case,
  ``multiplewordslikethis`` or ``multiple_words_like_this``.

* Do not choose ``camelCaseNames``, which are inconsistently
  capitalised.

Documenting code
++++++++++++++++

* Every module, class, and function has a Python doc string explaining
  its purpose and API.

  *Exception*: Functions whose purpose and API are mandated by Python
  itself (dunder-named methods) do not need a doc string.

* Every doc string conforms to :PEP:`257`. Additionally:

  * The text of the doc string is marked up with reStructuredText.

  * The first line is a one-line synopsis of the object. This summary
    line appears on the same line as the opening triple-quote,
    separated by a single space.

  * Further lines, if needed, are separated from the first by one
    blank line.

  * The synopsis is separated by one space from the opening
    triple-quote; this causes it to appear four columns past the
    beginning of the line. All subsequent lines are indented at least
    four columns also.

  * The synopsis is followed by a reStructuredText field list. The
    field names are: “param foo” for each parameter (where “foo” is
    the parameter name), and “return” for the return value. The field
    values describe the purpose of each.

  * The closing triple-quote appears on a separate line.

  Example::

    def frobnicate(spam, algorithm="dv"):
        """ Perform frobnication on the `spam` travortionate.

            :param spam: A travortionate (as a sequence of strings).
            :param algorithm: The name of the algorithm to use for
                frobnicating the travortionate.
            :return: The frobnicated travortionate, if it is
                non-empty; otherwise ``None``.

            The frobnication is done by the Dietzel-Venkman algorithm,
            and optimises for the case where `spam` is freebled and
            agglutinative.
            """
        spagnify(spam)
        # …

Import statements
+++++++++++++++++

* All ``import`` statements appear at the top of the module.

* Each ``import`` statement imports a single module, or (using
  ``from``) multiple names from a single module.

  Example::

    import sys
    import os
    from spam import (foo, bar, baz)

Additional style guidelines
+++++++++++++++++++++++++++

* All text files (including program code) are encoded in UTF-8.

* A page break (``U+000C FORM FEED``) whitespace character is used
  within a text file to break up semantically separate areas of the
  module.

* Editor hints for Emacs and Vim appear in a comment block at the
  file's end.

  For Python source code::

      
      # Local variables:
      # coding: utf-8
      # mode: python
      # End:
      # vim: fileencoding=utf-8 filetype=python :

  For reStructuredText documents::

      
      # Local variables:
      # coding: utf-8
      # mode: rst
      # mode: text
      # End:
      # vim: fileencoding=utf-8 filetype=rst :


Unit tests
==========

All code should aim for 100% coverage by unit tests. New code, or
changes to existing code, will only be considered for inclusion in the
development tree when accompanied by corresponding additions or
changes to the unit tests.

Test-driven development
-----------------------

Where possible, practice test-driven development to implement program
code.

* During a development session, maintain a separate window or terminal
  with the unit test suite for the project running continuously, or
  automatically every few seconds.

* Any time a test is failing, the only valid change is to make all
  tests pass.

* Develop new interface features (changes to the program unit's
  behaviour) only when all current tests pass.

* Refactor as needed, but only when all tests pass.

  * Refactoring is any change to the code which does not alter its
    interface or expected behaviour, such as performance
    optimisations, readability improvements, modularisation
    improvements etc.

* Develop new or changed program behaviour by:

  * *First* write a single, specific test case for that new behaviour,
    then watch the test fail in the absence of the desired behaviour.

  * Implement the minimum necessary change to satisfy the failing
    test. Continue until all tests pass again, then stop making
    functional changes.

  * Once all tests (including the new test) pass, consider refactoring
    the code and the tests immediately, then ensure all the tests pass
    again after any changes.

  * Iterate for each incremental change in interface or behaviour.

Test-driven development is not absolutely necessary, but is the
simplest, most direct way to generate the kind of program changes
accompanied by unit tests that are necessary for inclusion in the
project.


..
    This document is written using `reStructuredText`_ markup, and can
    be rendered with `Docutils`_ to other formats.

    ..  _Docutils: https://docutils.sourceforge.io/
    ..  _reStructuredText: https://docutils.sourceforge.io/rst.html

..
    This is free software: you may copy, modify, and/or distribute this work
    under the terms of the Apache License version 2.0 as published by the
    Apache Software Foundation.
    No warranty expressed or implied. See the file ‘LICENSE.ASF-2’ for details.

..
    Local variables:
    coding: utf-8
    mode: rst
    mode: text
    time-stamp-format: "%:y-%02m-%02d"
    time-stamp-start: "^:Updated:[	 ]+"
    time-stamp-end: "$"
    time-stamp-line-limit: 20
    End:
    vim: fileencoding=utf-8 filetype=rst :
