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Style Commandments

General

  • Optimize for readability; whitespace is your friend.
  • Put two newlines between top-level code (funcs, classes, etc.)
  • Put one newline between methods in classes and anywhere else.
  • Use blank lines to group related logic.
  • Never write except: (use except Exception: instead, at the very least).
  • All classes must inherit from object (explicitly).
  • Use single-quotes for strings unless the string contains a single-quote.
  • Use the double-quote character for blockquotes (""", not ''')
  • USE_ALL_CAPS_FOR_GLOBAL_CONSTANTS

Comments

  • In general use comments as "memory pegs" for those coming after you up the trail.
  • Guide the reader though long functions with a comments introducing different sections of the code.
  • Choose clean, descriptive names for functions and variables to make them self-documenting.
  • Include your name with TODOs as in # TODO(termie): blah blah....
  • Add # NOTE(termie): blah blah... comments to clarify your intent, or to explain a tricky algorithm, when it isn't obvious from just reading the code.

Identifiers

  • Do not give anything the same name as a built-in or reserved word.
  • Don't use single characters in identifiers except in trivial loop variables and mathematical algorithms.
  • Avoid abbreviations, especially if they are ambiguous or their meaning would not be immediately clear to the casual reader or newcomer.

Wrapping

Wrap long lines by using Python's implied line continuation inside parentheses, brackets and braces. Make sure to indent the continued line appropriately. The preferred place to break around a binary operator is after the operator, not before it.

Example:

class Rectangle(Blob):

    def __init__(self, width, height,
                 color='black', emphasis=None, highlight=0):

        # More indentation included to distinguish this from the rest.
        if (width == 0 and height == 0 and
                color == 'red' and emphasis == 'strong' or
                highlight > 100):
            raise ValueError('sorry, you lose')

        if width == 0 and height == 0 and (color == 'red' or
                                           emphasis is None):
            raise ValueError("I don't think so -- values are %s, %s" %
                             (width, height))

        msg = ('this is a very long string that goes on and on and on and'
               'on and on and on...')

        super(Rectangle, self).__init__(width, height,
                                        color, emphasis, highlight)

Imports

  • Only modules may be imported
  • Do not make relative imports
  • Order your imports by the full module path
  • Classes and functions may be hoisted into a package namespace, via __init__ files, with some discretion.
  • Organize your imports according to the template given below

Template:

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

Human Alphabetical Order Examples

Example:

import logging
import time
import unittest

import simplejson as json

import eom.common
from eom import test
import eom.util

More Import Examples

INCORRECT

import marconi.transport.wsgi as wsgi

CORRECT

from marconi.transport import wsgi

Docstrings

Docstrings are required for all functions and methods.

Docstrings should ONLY use triple-double-quotes (""")

Single-line docstrings should NEVER have extraneous whitespace between enclosing triple-double-quotes.

INCORRECT

""" There is some whitespace between the enclosing quotes :( """

CORRECT

"""There is no whitespace between the enclosing quotes :)"""

Docstrings should document default values for named arguments if they're not None

Docstrings that span more than one line should look like this:

Example:

"""Single-line summary, right after the opening triple-double-quote.

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

:param foo: the foo parameter
:param bar: (Default True) the bar parameter
:param foo_long_bar: the foo parameter description is very
  long so we have to split it in multiple lines in order to
  keey things ordered
:returns: return_type -- description of the return value
:returns: description of the return value
:raises: AttributeError, KeyError
"""

DO NOT leave an extra newline before the closing triple-double-quote.

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",
    },
}

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)

Internationalization (i18n) Strings

In order to support multiple languages, we have a mechanism to support automatic translations of exception and log strings.

Example:

msg = _("An error occurred")
raise HTTPBadRequest(explanation=msg)

If you have a variable to place within the string, first internationalize the template string then do the replacement.

Example:

msg = _("Missing parameter: %s") % ("flavor",)
LOG.error(msg)

If you have multiple variables to place in the string, use keyword parameters. This helps our translators reorder parameters when needed.

Example:

msg = _("The server with id %(s_id)s has no key %(m_key)s")
LOG.error(msg % {"s_id": "1234", "m_key": "imageId"})

Creating Unit Tests

For every any change, 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.

NOTE: 100% coverage is required

openstack-common

A number of modules from openstack-common are imported into the project.

These modules are "incubating" in openstack-common and are kept in sync with the help of openstack-common's update.py script. See:

http://wiki.openstack.org/CommonLibrary#Incubation

The copy of the code should never be directly modified here. Please always update openstack-common first and then run the script to copy the changes across.

Logging

Use __name__ as the name of your logger and name your module-level logger objects 'LOG':

LOG = logging.getLogger(__name__)