hacking is a set of flake8 plugins that test and enforce the OpenStack Style Guidlines.


hacking is available from pypi, so just run:

pip install hacking

This will install flake8 with the hacking and pyflake plugins


Most of the additional style guidelines that OpenStack has taken on came from the Google Python Style Guide.

Since then, a few more OpenStack specific ones have been added or modified.


hacking uses the major.minor.maintenance release notation, where maintenance releases cannot contain new checks. This way projects can gate on hacking by pinning on the major.minor number while accepting maintenance updates without being concerned that a new version will break the gate with a new check.

Adding additional checks

Each check is a pep8 plugin so read


  • The check must already have community support. We do not want to dictate style, only enforce it.
  • The canonical source of the OpenStack Style Guidelines is HACKING.rst, and hacking just enforces them; so when adding a new check, it must be in HACKING.rst
  • False negatives are ok, but false positives are not
  • Cannot be project specific, project specific checks should be Local Checks
  • Docstring tests
  • Registered as entry_points in setup.cfg
  • Error code must be in the relevant Hxxx group

Local Checks

hacking supports having local changes in a source tree. They can be configured to run in two different ways. They can be registered individually, or with a factory function.

For individual registration, put a comma separated list of pep8 compatible check functions into the hacking section of tox.ini. E.g.:

local-check = nova.tests.hacking.bad_code_is_terrible

Alternately, you can specify the location of a callable that will be called at registration time and will be passed the registration function. The callable should expect to call the passed in function on everything if wants to register. Such as:

local-check-factory = nova.tests.hacking.factory

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