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Code Guidelines
---------------
A few code guidelines to try to stick to, please comment if none of these make
sense, they are pretty basic and mostly apply to old code. However for people
who are looking at current code, they make take up bad habits that exist in the
current codebase.
Python Version
--------------
Python 2.6 is the minimum supported version, since it is the first version to
support Python 3 syntax. All exception handling should use Python 3 'except'
syntax, and the print function should be used instead of Python 2's print
statement (from __future__ import print_function).
Dependencies
------------
Python and Bash should be the only hard dependencies. Any other dependencies,
including external Python modules that are not included with Python itself,
must be optionally enabled by run-time detection.
Tabs
----
The current code uses tabs, not spaces. Keep whitespace usage consistent
between files. New files should use tabs.
Line-Wrapping
-------------
Lines should typically not be longer than 80 characters; if they are an attempt
should be made to wrap them. Move code to the line below and indent once (\t).
errors.append(MalformedMetadata(
errors.DESCRIPTION_TOO_LONG_ERROR % \
(length, max_desc_len),
attr='DESCRIPTION.toolong')
Do not do this:
errors.append(MalformedMetadata(
errors.DESCRIPTION_TOO_LONG_ERROR % \
(length, max_desc_len),
attr='DESCRIPTION.toolong')
The mixing of tabs and spaces means other developers can't read what you did.
This is why the python peps state spaces over tabs; because with spaces the line
wrapping is always clear (but you cannot convert spaces as easily as tabwidth).
Comparisons
-----------
if foo != None
should be replaced with:
if foo is not None:
Is not does a reference comparison (address1 = address2 basically) and
the == forces a by value compare (with __eq__())
Dict Lookups
------------
Try not to use has_key, you can use
if foo in dict
instead of if dict.has_key(foo)
Also don't do stuff like:
if foo in dict and dict[foo]:
Generally you can do two things here, if you are messing with defaults..
dict.get(foo, some_default)
will try to retrieve foo from dict, if there is a KeyError, will insert foo
into dict with the value of some_default. This method is preferred in cases where
you are messing with defaults:
try:
dict[foo]
except KeyError:
dict[foo] = default_value
The get call is nicer (compact) and faster (try,except are slow).
Exceptions
----------
Don't use the format raise Exception, "string"
It will be removed in py3k.
YES:
raise KeyError("No key")
NO:
raise KeyError, "No key"
Imports
-------
Import things one per line
YES:
import os
import time
import sys
NO:
import os,sys,time
When importing from a module, you may import more than 1 thing at a time.
YES:
from portage.module import foo, bar, baz
Multiline imports are ok (for now :))
Try to group system and package imports separately.
YES:
import os
import sys
import time
from portage.locks import lockfile
from portage.versions import vercmp
NO:
import os
import portage
import portage.util
import time
import sys
Try not to import large numbers of things into the namespace of a module.
I realize this is done all over the place in current code but it really makes it
a pain to do code reflection when the namespace is cluttered with identifiers
from other modules.
YES:
from portage import output
NO:
from portage.output import bold, create_color_func, darkgreen, \
green, nocolor, red, turquoise, yellow
The YES example imports the 'output' module into the current namespace.
The negative here is having to use output.COLOR all over the place instead of
just COLOR. However it means during introspection of the current namespace
'green','red', 'yellow', etc. will not show up.
The NO example just imports a set of functions from the output module. It is
somewhat annoying because the import line needs to be modified when functions
are needed and often unused functions are left in the import line until someone
comes along with a linter to clean up (does not happen often).
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