salt/doc/topics/style.rst
2013-04-30 14:15:26 -06:00

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=================
Salt Coding Style
=================
Salt is developed with a certain coding style, while the style is dominantly
PEP 8 it is not completely PEP 8. It is also noteworthy that a few
development techniques are also employed which should be adhered to. In the
end, the code is made to be "Salty".
Most importantly though, we will accept code that violates the coding style and
KINDLY ask the contributor to fix it, or go ahead and fix the code on behalf of
the contributor. Coding style is NEVER grounds to reject code contributions,
and is never grounds to talk down to another member of the community (There are
no grounds to treat others without respect, especially people working to
improve Salt)!!
Strings
=======
Salt follows a few rules when formatting strings:
Single Quotes
-------------
In Salt, all strings use single quotes unless there is a good reason not to.
This means that docstrings use single quotes, standard strings use single
quotes etc.:
.. code-block:: python
def foo():
'''
A function that does things
'''
name = 'A name'
return name
Formatting Strings
------------------
All strings which require formatting should use the `.format` string method:
.. code-block:: python
data = 'some text'
more = '{0} and then some'.format(data)
Make sure to use indices or identifiers in the format brackets, since empty
brackets are not supported by python 2.6.
Please do NOT use printf formatting.
Docstring Conventions
---------------------
Docstrings should always add a newline, docutils takes care of the new line and
it makes the code cleaner and more vertical:
`GOOD`:
.. code-block:: python
def bar():
'''
Here lies a docstring with a newline after the quotes and is the salty
way to handle it! Vertical code is the way to go!
'''
return
`BAD`:
.. code-block:: python
def baz():
'''This is not ok!'''
return
Imports
=======
Salt code prefers importing modules and not explicit functions. This is both a
style and functional preference. The functional preference originates around
the fact that the module import system used by pluggable modules will include
callable objects (functions) that exist in the direct module namespace. This
is not only messy, but may unintentionally expose code python libs to the Salt
interface and pose a security problem.
To say this more directly with an example, this is `GOOD`:
.. code-block:: python
import os
def minion_path():
path = os.path.join(self.opts['cachedir'], 'minions')
return path
This on the other hand is `DISCOURAGED`:
.. code-block:: python
from os.path import join
def minion_path():
path = join(self.opts['cachedir'], 'minions')
return path
The time when this is changed is for importing exceptions, generally directly
importing exceptions is preferred:
This is a good way to import exceptions:
.. code-block:: python
from salt.exceptions import CommandExecutionError
Vertical is Better
==================
When writing Salt code, vertical code is generally preferred. This is not a hard
rule but more of a guideline. As PEP 8 specifies, Salt code should not exceed 79
characters on a line, but it is preferred to separate code out into more
newlines in some cases for better readability:
.. code-block:: python
import os
os.chmod(
os.path.join(self.opts['sock_dir'],
'minion_event_pub.ipc'),
448
)
Where there are more line breaks, this is also apparent when constructing a
function with many arguments, something very common in state functions for
instance:
.. code-block:: python
def managed(name,
source=None,
source_hash='',
user=None,
group=None,
mode=None,
template=None,
makedirs=False,
context=None,
replace=True,
defaults=None,
env=None,
backup='',
**kwargs):
Indenting
=========
Some confusion exists in the python world about indenting things like function
calls, the above examples use 8 spaces when indenting comma-delimited
constructs.
The confusion arises because the pep8 program INCORRECTLY flags this as wrong,
where PEP 8, the document, cites only using 4 spaces here as wrong, as it
doesn't differentiate from a new indent level.
Right:
.. code-block:: python
def managed(name,
source=None,
source_hash='',
user=None)
WRONG:
.. code-block:: python
def managed(name,
source=None,
source_hash='',
user=None)
Lining up the indent is also correct:
.. code-block:: python
def managed(name,
source=None,
source_hash='',
user=None)
This also applies to function calls and other hanging indents.
pep8 and Flake8 (and, by extension, the vim plugin Syntastic) will complain
about the double indent for hanging indents. This is a `known conflict
<https://github.com/jcrocholl/pep8/issues/167#issuecomment-15936564>`_ between
pep8 (the script) and the actual PEP 8 standard. It is recommended that this
particular warning be ignored with the following lines in
:code:`~/.config/flake8`:
.. code-block:: ini
[flake8]
ignore = E226,E241,E242,E126
Make sure your Flake8/pep8 are up to date. The first three errors are ignored
by default and are present here to keep the behavior the same. This will also
work for pep8 without the Flake8 wrapper -- just replace all instances of
'flake8' with 'pep8', including the filename.
Code Churn
==========
Many pull requests have been submitted that only churn code in the name of
PEP 8. Code churn is a leading source of bugs and is strongly discouraged.
While style fixes are encouraged they should be isolated to a single file per
commit, and the changes should be legitimate, if there are any questions about
whether a style change is legitimate please reference this document and the
official PEP 8 (http://www.python.org/dev/peps/pep-0008/) document before
changing code. Many claims that a change is PEP 8 have been invalid, please
double check before committing fixes.