Code Reviews

Glance follows the same Review guidelines outlined by the OpenStack community. This page provides additional information that is helpful for reviewers of patches to Glance.


Glance uses the Gerrit tool to review proposed code changes. The review site is

Gerrit is a complete replacement for Github pull requests. All Github pull requests to the Cinder repository will be ignored.

See Quick Reference for information on quick reference for developers. See Getting Started for information on how to get started using Gerrit. See Development Workflow for more detailed information on how to work with Gerrit.

The Great Change

With the demise of Python 2.7 in January 2020, beginning with the Ussuri development cycle, Glance only needs to support Python 3 runtimes (in particular, 3.6 and 3.7). Thus we can begin to incorporate Python 3 language features and remove Python 2 compatibility code. At the same time, however, we are still supporting stable branches that must support Python 2. Our biggest interaction with the stable branches is backporting bugfixes, where in the ideal case, we’re just doing a simple cherry-pick of a commit from master to the stable branches. You can see that there’s some tension here.

With that in mind, here are some guidelines for reviewers and developers that the Glance community has agreed on during this phase where we want to write pure Python 3 but still must support Python 2 code.

Python 2 to Python 3 transition guidelines

  • We need to be checking the code coverage of test cases very carefully so that new code has excellent coverage. The idea is that we want these tests to fail when a backport is proposed to a stable branch and the tests are run under Python 2 (if the code is using any Python-3-only language features).

  • New features can use Python-3-only language constructs, but bugfixes likely to be backported should be more conservative and write for Python 2 compatibilty.

  • The code for drivers may continue to use the six compatibility library at their discretion.

  • We will not remove six from mainline Cinder code that impacts the drivers (for example, classes they inherit from).

  • We can remove six from code that doesn’t impact drivers, keeping in mind that backports may be more problematic, and hence making sure that we have really good test coverage.

Unit Tests

Glance requires unit tests with all patches that introduce a new branch or function in the code. Changes that do not come with a unit test change should be considered closely and usually returned to the submitter with a request for the addition of unit test.