python-mcollective style guide

This guide is highly inspired on OpenStack guidelines.

General

  • Use only UNIX style newlines (\n), not Windows style (\r\n)

  • Wrap long lines in parentheses and not a backslash for line continuation.

  • Do not write except:, use except Exception: at the very least

  • Include your name with TODOs as in #TODO(yourname)

  • Do not shadow a built-in or reserved word. Example:

    def list():
    return [1, 2, 3]

mylist = list() # BAD, shadows `list` built-in

class Foo(object):
    def list(self):
        return [1, 2, 3]

mylist = Foo().list() # OKAY, does not shadow built-in

  • Use the is not operator when testing for unequal identities. Example:

    if not X is Y:  # BAD, intended behavior is ambiguous
    pass

if X is not Y:  # OKAY, intuitive
    pass

  • Use the not in operator for evaluating membership in a collection. Example:

    if not X in Y:  # BAD, intended behavior is ambiguous
    pass

if X not in Y:  # OKAY, intuitive
    pass

if not (X in Y or X in Z):  # OKAY, still better than all those 'not's
    pass

Imports

  • Do not import objects, only modules (*)
  • Do not import more than one module per line
  • Do not use wildcard * import
  • Order your imports by the full module path
  • Organize your imports according to the following template

(*) exceptions are:

  • imports from . package

Example:

{{stdlib imports in human alphabetical order}}
\n
{{third-party lib imports in human alphabetical order}}
\n
{{project imports in human alphabetical order}}
\n
\n
{{begin your code}}

Human Alphabetical Order Examples

Example:

import httplib
import logging
import random
import StringIO
import time
import unittest

import eventlet
import webob.exc

import nova.api.ec2
from nova.api import openstack
from nova.auth import users
from nova.endpoint import cloud
import nova.flags
from nova import test

Docstrings

Example:

"""A one line docstring looks like this and ends in a period."""


"""A multi line docstring has a one-line summary, less than 80 characters.

Then a new paragraph after a newline that explains in more detail any
general information about the function, class or method. Example usages
are also great to have here if it is a complex class for function.

When writing the docstring for a class, an extra line should be placed
after the closing quotations. For more in-depth explanations for these
decisions see http://www.python.org/dev/peps/pep-0257/

If you are going to describe parameters and return values, use Sphinx, the
appropriate syntax is as follows.

:arg str foo: the foo parameter of type :py:class:`str`
:param bar: the bar parameter
:returns: return_type -- description of the return value
:returns: description of the return value
:raises: AttributeError, KeyError
"""

Dictionaries/Lists

If a dictionary (dict) or list object is longer than 80 characters, its items should be split with newlines. Embedded iterables should have their items indented. Additionally, the last item in the dictionary should have a trailing comma. This increases readability and simplifies future diffs.

Example:

my_dictionary = {
    "image": {
        "name": "Just a Snapshot",
        "size": 2749573,
        "properties": {
            "user_id": 12,
            "arch": "x86_64",
        },
        "things": [
            "thing_one",
            "thing_two",
        ],
        "status": "ACTIVE",
    },
}

Do not use locals() for formatting strings, it is not clear as using explicit dictionaries and can hide errors during refactoring.

Calling Methods

Calls to methods 80 characters or longer should format each argument with newlines. This is not a requirement, but a guideline:

unnecessarily_long_function_name('string one',
                                 'string two',
                                 kwarg1=constants.ACTIVE,
                                 kwarg2=['a', 'b', 'c'])

Rather than constructing parameters inline, it is better to break things up:

list_of_strings = [
    'what_a_long_string',
    'not as long',
]

dict_of_numbers = {
    'one': 1,
    'two': 2,
    'twenty four': 24,
}

object_one.call_a_method('string three',
                         'string four',
                         kwarg1=list_of_strings,
                         kwarg2=dict_of_numbers)

Creating Unit Tests

For every new feature, unit tests should be created that both test and (implicitly) document the usage of said feature. If submitting a patch for a bug that had no unit test, a new passing unit test should be added. If a submitted bug fix does have a unit test, be sure to add a new one that fails without the patch and passes with the patch.

Commit Messages

Using a common format for commit messages will help keep our git history readable. Follow these guidelines:

First, provide a brief summary of 50 characters or less. Summaries of greater then 72 characters will be rejected by the gate.

The first line of the commit message should provide an accurate description of the change, not just a reference to an issue. It must not end with a period and must be followed by a single blank line.

Following your brief summary, provide a more detailed description of the patch, manually wrapping the text at 72 characters. This description should provide enough detail that one does not have to refer to external resources to determine its high-level functionality.

For further information on constructing high quality commit messages, and how to split up commits into a series of changes, consult the OpenStack project wiki:

Flake8

As part of Travis-CI tests setup, flake8 is being ran, so any style problem will make tests fail and no changes will integrated until the problem is fixed.