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Python coding style guide for Mailman
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Copyright (C) 2002-2004 Barry A. Warsaw
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NOTE: The canonical version of this style guide can be found at:
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http://barry.warsaw.us/software/STYLEGUIDE.txt
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This document contains a style guide for Python programming, as used in
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Mailman. In general, Guido van Rossum's style guide should be taken as a
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basis, as embodied in PEP 8:
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http://www.python.org/peps/pep-0008.html
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however, my (Barry Warsaw's) personal preferences differ from Guido's in a few
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places. "When in Rome..." should apply meaning, when coding stuff for Python,
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Guido's style should rule, however when coding for Mailman, I'd like to see my
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preferences used instead.
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Remember rule #1, A Foolish Consistency is the Hobgoblin of Little Minds.
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That said, here's a quick outline of where my preferences depart from Guido's:
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- Imports usually should be on separate lines. While it's sometimes
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from types import StringType, ListType
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it's never okay to say
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Put these on separate lines.
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- Imports are always put at the top of the file, just after any module
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comments and docstrings, and before module globals and constants.
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Imports should be grouped, with the order being:
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1. standard library imports
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2. related major package imports (i.e. all email package imports next)
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3. application specific imports
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From-imports should follow non-from imports. Dotted imports should follow
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non-dotted imports. Non-dotted imports should be grouped by increasing
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length, while dotted imports should be grouped roughly alphabetically.
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- In general, there should be at most one class per module, if the module
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contains class definitions. If it's a module of functions, that's fine,
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group them as common sense dictates. A class-containing module can also
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contain some helper functions, but it's best to keep these non-public
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(i.e. use a single leading underscore).
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Always give the class and the module the same name, differing only by case
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as PEP 8 recommends. E.g.
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from mailman.parser import Parser
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- When importing a class from a class-containing module, it's usually
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from myclass import MyClass
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from foo.bar.yourclass import YourClass
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If this spelling causes name clashes, then spell them
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import foo.bar.yourclass
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and use "myclass.MyClass"
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- Right hanging comments are discouraged, in favor of preceding comments.
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foo = blarzigop(bar) # if you don't blarzigop it, it'll shlorp
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# if you don't blarzigop it, it'll shlorp
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- Major sections of code in a module should be separated by line feed
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characters (e.g. ^L -- that's a single character control-L not two
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characters). This helps with Emacs navigation.
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Always put a ^L before module-level functions, before class definitions,
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before big blocks of constants which follow imports, and any place else that
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would be convenient to jump to. Always put two blank lines before a ^L.
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- Put to blank lines between any module level function. Put only one blank
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line between methods in a class. No blank lines between the class
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definition and the first method in the class (although class docstrings
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often go in this space).
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- Try to minimize the vertical whitespace in a class. If you're inclined to
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separate stanzas of code for readability, consider putting a comment in
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describing what the next stanza's purpose is. Don't put stupid or obvious
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comments in just to avoid vertical whitespace though.
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- Unless internal quote characters would mess things up, the general rule is
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that single quotes should be used for short strings, double quotes for
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triple-quoted multi-line strings and docstrings. E.g.
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warn = "Don't mess things up"
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notice = """Our three chief weapons are:
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- an almost fanatical devotion to the pope
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- Write docstrings for all public modules, functions, classes, and methods.
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Docstrings are not necessary and usually discouraged for non-public methods,
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but you should have a comment that describes what the method does. This
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comment should appear after the "def" line.
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- PEP 257 describes good docstrings conventions. Note that most importantly,
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the """ that ends a multiline docstring should be on a line by itself, e.g.:
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Optional plotz says to frobnicate the bizbaz first.
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- For one liner docstrings, keep the closing """ on the same line --
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except for module docstrings!
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- <> is strongly preferred over !=
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- fill-column for docstrings should be 78.
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- Always use string methods instead of string module functions.
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- For sequences, (strings, lists, tuples), use the fact that empty sequences
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are false, so "if not seq" or "if seq" is preferable to "if len(seq)" or "if
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not len(seq)". Always use True and False instead of 1 and 0 for boolean
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- Always decide whether a class's methods and instance variables should be
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public or non-public. In general, never make data variables public unless
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you're implementing essentially a record. It's almost always preferable to
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give a functional interface to your class instead (Python 2.2's descriptors
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and properties make this much nicer).
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Also decide whether your attributes should be private or not. The
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difference between private and non-public is that the former will never be
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useful for a derived class, while the latter might be. Yes, you should
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design your classes with inheritance in mind!
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- Single leading underscores are generally preferred for non-public
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attributes. Use double leading underscores only in classes designed for
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inheritance to ensure that truly private attributes will never name clash.
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Public attributes should have no leading or trailing underscores unless they
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conflict with reserved words, in which case, a single trailing underscore is
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preferable to a leading one, or a corrupted spelling, e.g. class_ rather
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