neutron-vpnaas/HACKING.rst

Neutron Style Commandments

• Step 1: Read http://www.python.org/dev/peps/pep-0008/
• Step 2: Read http://www.python.org/dev/peps/pep-0008/ again
• Step 3: Read on

General

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

• Put one newline between methods in classes and anywhere else

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

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

• 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

Imports

• Do not make relative imports
• Order your imports by the full module path

Example:

The following imports,

from neutron.api import networks
from neutron import wsgi

are considered equivalent for ordering purposes to

import neutron.api.networks
import neutron.wsgi

• Organize your imports according to the following template

Example:

# vim: tabstop=4 shiftwidth=4 softtabstop=4
{{stdlib imports in human alphabetical order}}
\n
{{third-party lib imports in human alphabetical order}}
\n
{{neutron imports in human alphabetical order}}
\n
\n
{{begin your code}}

Human Alphabetical Order Examples

Example:

import httplib
import random
import StringIO
import time

import eventlet
import testtools
import webob.exc

import neutron.api.networks
from neutron.api import ports
from neutron.db import models
from neutron.extensions import multiport
import neutron.manager
from neutron.openstack.common import log as logging
from neutron import service

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/

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: 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",
    },
}

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"})

Please do not use locals() for string substitutions.

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.

All unittest classes must ultimately inherit from testtools.TestCase. In the Neutron test suite, this should be done by inheriting from neutron.tests.base.BaseTestCase.

All setUp and tearDown methods must upcall using the super() method. tearDown methods should be avoided and addCleanup calls should be preferred. Never manually create tempfiles. Always use the tempfile fixtures from the fixture library to ensure that they are cleaned up.

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.