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Keystone Style Commandments

General

  • Put two newlines between top-level code (funcs, classes, etc)

  • Put one newline between methods in classes and anywhere else

  • Long lines should be wrapped in parentheses in preference to using a backslash for line continuation.

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

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

  • Do not name anything the same name as a built-in or reserved word

  • When defining global constants, define them before functions and classes

  • Avoid using "double quotes" where you can reasonably use 'single quotes'

  • 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

TODO vs FIXME

  • TODO(name): implies that something should be done (cleanup, refactoring, etc), but is expected to be functional.
  • FIXME(name): implies that the method/function/etc shouldn't be used until that code is resolved and bug fixed.

Logging

Use the built-in logging module, and ensure you getLogger:

from keystone.common import logging

LOG = logging.getLogger(__name__)

LOG.debug('Foobar')

Imports

  • Import modules, not module attributes
  • Do not import more than one module per line
  • Do not make relative imports
  • Order your imports by the full module path
  • Organize your imports according to the following template

Example:

# vim: tabstop=4 shiftwidth=4 softtabstop=4
{{stdlib imports ordered by full module path}}
\n
{{third-party lib imports ordered by full module path}}
\n
{{nova imports ordered by full module path}}
\n
\n
{{begin your code}}

Import by Full Module Path 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 ldap
from nova.auth import users
from nova.endpoint import cloud
import nova.flags
from nova import test
from nova import utils

Docstrings

Example:

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


"""A multiline 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/

A docstring ends with an empty line before the closing quotations.

Describe parameters and return values, using the Sphinx format; the
appropriate syntax is as follows.

:param foo: the foo parameter
:param bar: the bar parameter
:type bar: parameter type for 'bar'
: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",
    },
}

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 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.

For more information on creating unit tests and utilizing the testing infrastructure in OpenStack Nova, please read nova/testing/README.rst.

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.