============================== GNU Mailman Coding Style Guide ============================== Copyright (C) 2002-2019 Barry Warsaw Python coding style guide for GNU Mailman ========================================= *NOTE*: The canonical version of this style guide can be found at: http://barry.warsaw.us/software/STYLEGUIDE.txt This document contains a style guide for Python programming, as used in GNU Mailman. `PEP 8`_ is the basis for this style guide so it's recommendations should be followed except for the differences outlined here. This document assumes the use of Python 3. * Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants, but after any ``__future__`` imports, or ``__metaclass__`` and ``__all__`` definitions. Imports should be grouped, with the order being: 1. non-from imports for standard and third party libraries 2. non-from imports from the application 3. from-imports from the standard and third party libraries 4. from-imports from the application From-imports should follow non-from imports. Dotted imports should follow non-dotted imports. Non-dotted imports should be grouped by increasing length, while dotted imports should be grouped alphabetically. See this flake8 plugin for enforcement of these rules: https://gitlab.com/warsaw/flufl.flake8 * In general, there should be one class per module. Keep files small, but it's okay to group related code together. List everything exported from the module in the ``__all__``. This library makes this very easy: https://pypi.org/project/atpublic/ * Right hanging comments are discouraged, in favor of preceding comments. E.g. bad:: foo = blarzigop(bar) # if you don't blarzigop it, it'll shlorp Good:: # If you don't blarzigop it, it'll shlorp. foo = blarzigop(bar) Comments should always be complete sentences, with proper capitalization and full stops at the end. * Put two blank lines between any top level construct or block of code (e.g. after import blocks). Put only one blank line between methods in a class. No blank lines between the class definition and the first method in the class. No blank lines between a class/method and its docstrings. * Try to minimize the vertical whitespace in a class or function. If you're inclined to separate stanzas of code for readability, consider putting a comment in describing what the next stanza's purpose is. Don't put stupid or obvious comments in just to avoid vertical whitespace though. * Unless internal quote characters would mess things up, the general rule is that single quotes should be used for short strings, double quotes for triple-quoted multi-line strings and docstrings. E.g.:: foo = 'a foo thing' warn = "Don't mess things up" notice = """Our three chief weapons are: - surprise - deception - an almost fanatical devotion to the pope """ * Write docstrings for modules, functions, classes, and methods. Docstrings can be omitted for special methods (e.g. __init__() or __str__()) where the meaning is obvious. * PEP 257 describes good docstrings conventions. Note that most importantly, the """ that ends a multiline docstring should be on a line by itself, e.g.:: """Return a foobang Optional plotz says to frobnicate the bizbaz first. """ * For one liner docstrings, keep the closing """ on the same line. * ``fill-column`` for docstrings should be 78. * When testing the emptiness of sequences, use ``if len(seq) == 0`` instead of relying on the falseness of empty sequences. However, if a variable can be one of several false values, it's okay to just use ``if seq``, though a preceding comment is usually in order. * Always decide whether a class's methods and instance variables should be public or non-public. Single leading underscores are generally preferred for non-public attributes. Use double leading underscores only in classes designed for inheritance to ensure that truly private attributes will never name clash. These should be rare. Public attributes should have no leading or trailing underscores unless they conflict with reserved words, in which case, a single trailing underscore is preferable to a leading one, or a corrupted spelling, e.g. ``class_`` rather than ``klass``. .. _`PEP 8`: http://www.python.org/peps/pep-0008.html .. _`GNU Mailman Python template`: http://bazaar.launchpad.net/~mailman-coders/mailman/3.0/annotate/head%3A/template.py