If you're here to make a change to ‘recipes’ (the code located in scripts/slave/recipes*), please take a look at the README for more information pertaining to recipes.
The preferred style is PEP8 with two-space indent; that is, the Chromium Python style. Functions use lowercase_with_underscores, with the exception of the special functions RunSteps and RunTests in recipes. Use yapf (git cl format) to autoformat new code.