These rules are fairly standard and boring. People will bitch about something in here, no doubt. Get over it. Much of this was stolen from the Linux Kernel coding style, because most of it makes good sense. If you disagree, that's OK, but please stick to the rules anyway ;-)


Please use Python where possible. It‘s not the ideal language for everything, but it’s pretty good, and consistency goes a long way in making the project maintainable. (Obviously using C or whatever for writing tests is fine).

Base coding style

When writing python code, unless otherwise stated, stick to the python style guide (

Indentation & whitespace

Format your code for an 80 character wide screen.

Indentation is now 4 spaces, as opposed to hard tabs (which it used to be). This is the Python standard.

For hanging indentation, use 8 spaces plus all args should be on the new line.

 # Either of the following hanging indentation is considered acceptable.

YES: return ‘class: %s, host: %s, args = %s’ % (, self.hostname, self.args)

YES: return ‘class: %s, host: %s, args = %s’ % (, self.hostname, self.args)

 # Do not use 4 spaces for hanging indentation

NO: return ‘class: %s, host: %s, args = %s’ % (, self.hostname, self.args)

 # Do put all args on new line

NO: return ‘class: %s, host: %s, args = %s’ % (, self.hostname, self.args)

Don't leave trailing whitespace, or put whitespace on blank lines.

Leave TWO blank lines between functions - this is Python, there are no clear function end markers, and we need help.

Variable names and UpPeR cAsE

Use descriptive variable names where possible - it helps to make the code self documenting.

Don‘t use CamelCaps style in most places - use underscores to separate parts of your variable_names please. I shall make a bedgrudging exception for class names I suppose, but I’ll still whine about it a lot.

Importing modules

The order of imports should be as follows:

Standard python modules Non-standard python modules Autotest modules

Within one of these three sections, all module imports using the from keyword should appear after regular imports. Each module should be imported on its own line. Wildcard imports (from x import *) should be avoided if possible. Classes should not be imported from modules, but modules may be imported from packages, i.e.: from common_lib import error and not from common_lib.error import AutoservError

For example: import os import pickle import random import re import select import shutil import signal import subprocess

import common # Magic autotest_lib module and sys.path setup code. import MySQLdb # After common so that we check our site-packages first.

from common_lib import error

Testing None

Use “is None” rather than “== None” and “is not None” rather than “!= None”. This way you‘ll never run into a case where someone’s eq or ne method do the wrong thing


Generally, you want your comments to tell WHAT your code does, not HOW. We can figure out how from the code itself (or if not, your code needs fixing).

Try to describle the intent of a function and what it does in a triple-quoted (multiline) string just after the def line. We‘ve tried to do that in most places, though undoubtedly we’re not perfect. A high level overview is incredibly helpful in understanding code.

Hardcoded String Formatting

Strings should use only single quotes for hardcoded strings in the code. Double quotes are acceptable when single quote is used as part of the string. Multiline string should not use '' but wrap the string using parenthesises.

REALLY_LONG_STRING = ('This is supposed to be a really long string that is ' 'over 80 characters and does not use a slash to ' ‘continue.’)


Docstrings are important to keep our code self documenting. While it's not necessary to overdo documentation, we ask you to be sensible and document any nontrivial function. When creating docstrings, please add a newline at the beginning of your triple quoted string and another newline at the end of it. If the docstring has multiple lines, please include a short summary line followed by a blank line before continuing with the rest of the description. Please capitalize and punctuate accordingly the sentences. If the description has multiple lines, put two levels of indentation before proceeding with text. An example docstring:

def foo(param1, param2): """ Summary line.

Long description of method foo.

@param param1: A thing called param1 that is used for a bunch of stuff
        that has methods bar() and baz() which raise SpamError if
        something goes awry.

@returns a list of integers describing changes in a source tree

@raises exception that could be raised if a certain condition occurs.


The tags that you can put inside your docstring are tags recognized by systems like doxygen. Not all places need all tags defined, so choose them wisely while writing code. Generally (if applicable) always list parameters, return value (if there is one), and exceptions that can be raised to each docstring.

@author - Code author @param - Parameter description @raise - If the function can throw an exception, this tag documents the possible exception types. @raises - same as @raise. @return - Return value description @returns - Same as @return @see - Reference to what you have done @warning - Call attention to potential problems with the code @var - Documentation for a variable or enum value (either global or as a member of a class) @version - Version string

When in doubt refer to:

Simple code

Keep it simple; this is not the right place to show how smart you are. We have plenty of system failures to deal with without having to spend ages figuring out your code, thanks ;-) Readbility, readability, readability. I really don't care if other things are more compact.

“Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.” Brian Kernighan

Function length

Please keep functions short, under 30 lines or so if possible. Even though you are amazingly clever, and can cope with it, the rest of us are all stupid, so be nice and help us out. To quote the Linux Kernel coding style:

Functions should be short and sweet, and do just one thing. They should fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24, as we all know), and do one thing and do that well.


When raising exceptions, the preferred syntax for it is:

raise FooException(‘Exception Message’)

Please don‘t raise string exceptions, as they’re deprecated and will be removed from future versions of python. If you're in doubt about what type of exception you will raise, please look at and client/common_lib/, the former is a list of python built in exceptions and the later is a list of autotest/autoserv internal exceptions. Of course, if you really need to, you can extend the exception definitions on client/common_lib/

Submitting patches

Generate universal diffs. Email them to Most mailers now break lines and/or changes tabs to spaces. If you know how to avoid that - great, put your patches inline. If you‘re not sure, just attatch them, I don’t care much. Please base them off the current version.

Don‘t worry about submitting patches to a public list - everybody makes mistakes, especially me ... so get over it and don’t worry about it. (though do give your changes a test first ;-))