melange/HACKING

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

Imports
-------
- thou shalt not import objects, only modules
- thou shalt not import more than one module per line
- thou shalt not make relative imports
- thou shalt order your imports by the full module path
- thou shalt organize your imports according to the following template

::
  # vim: tabstop=4 shiftwidth=4 softtabstop=4
  {{stdlib imports in human alphabetical order by module name}}
  \n
  {{nova imports in human alphabetical order by module name}}
  \n
  \n
  {{begin your code}}


General
-------
- thou shalt put two newlines twixt toplevel code (funcs, classes, etc)
- thou shalt put one newline twixt methods in classes and anywhere else
- thou shalt not write "except:", use "except Exception:" at the very least
- thou shalt include your name with TODOs as in "TODO(termie)"
- thou shalt not name anything the same name as a builtin or reserved word
- thou shalt not violate causality in our time cone, or else


Human Alphabetical Order Examples
---------------------------------
::
  import httplib
  import logging
  import random
  import StringIO
  import time
  import unittest

  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
  :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",
        },
    }
  
  Only use the dict constructor for casting. Do not use it to create a new
  dictionary.

  Example (BAD):
    
    my_dictionary = dict(key1='param1', key2='param2', key3=['a', 'b'])


Defining Methods
----------------
  Method signatures longer than 80 characters are very unreadable. If you
  encounter this problem, first you should determine if your method is
  too big. Otherwise, you should compress your keyword arguments with a
  '**kwargs' parameter. You should use the 'kwargs' in your method as a
  dictionary to retrieve the necessary keyword arguments.

  Example (BAD):

    def my_method(argument_one, argument_two, kwarg_one='default_one',
                  kwarg_two='default_two', kwarg_three='default_three'):

  Example (GOOD): 

    def my_method(argumet_one, argument_two, **kwargs):
        kwarg_one = kwargs.get('kwarg_one', 'default_one')
        kwarg_two = kwargs.get('kwarg_one', 'default_one')
        kwarg_three = kwargs.get('kwarg_three', 'default_three')


Calling Methods
---------------
  Calls to methods 80 characters or longer should format each argument with 
  newlines. This is mainly for readability.

    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"))