Nova 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 name anything the same name as a built-in or reserved word Imports ------- - Do not import objects, only modules - 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 :: # vim: tabstop=4 shiftwidth=4 softtabstop=4 {{stdlib imports in human alphabetical order}} \n {{third-party lib imports in human alphabetical order}} \n {{nova imports in human alphabetical order}} \n \n {{begin your code}} Human Alphabetical Order Examples --------------------------------- :: 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 import nova.flags from nova.endpoint import cloud from nova import test Docstrings ---------- """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. After you have finished your descriptions add an extra newline and close the quotations. 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"})