Closed Bug 1471641 Opened 2 years ago Closed 2 years ago

[mozinstall] Add support for Python 3


(Testing :: Mozbase, enhancement, P3)

Version 2


(firefox66 fixed)

Tracking Status
firefox66 --- fixed


(Reporter: davehunt, Assigned: wlach, Mentored)



(Keywords: good-first-bug)


(4 files)

+++ This bug was initially created as a clone of Bug #1427062 +++

We need to add support for Python3 without losing legacy Python support. Whilst some aspects were taken care of in bug 1388018 we are now able to run the unit tests against Python 3, and many of these are failing.

To work on this bug you will need to install and configure Mercurial, which will enable you to download the Firefox source code. It will also be used to commit your changes locally and prepare a patch for review. See the installation guide at for help getting Mercurial on your system. Once installed, there are some extensions we recommend installing, details of these can be found here:

To clone the Firefox source code we recommend using the unified repository. Details of this and how to create a bookmark for your work can be found here:

As this bug relates to Python 3, you will need to have this installed on your system. Our continuous integration is currently using Python 3.5, so for best results we recommend using the same version locally. There are a number of ways to install Python, and they vary depending on your environment. We suggest reading over the guides at to find the best method for you. Note that we also need to maintain support for Python 2, so you'll also need to have Python 2.7 installed.

Whilst we're moving towards adding support for Python 3, we've disabled any tests that fail against this version. This means that in order to work on this bug you will need to enable the tests. This can be done by removing "skip-if = python == 3" from the manifest file in `testing/mozbase/mozinstall/tests/manifest.ini`

To run the tests against Python 3, execute the following command:

mach python-test --python=3.5 testing/mozbase/mozinstall

Work through the test failures, and update the tests and source code for the package to simultaneously support Python 2.7 and Python 3.5. You can always check that your changes have not inadvertently broken support for Python 2 by using `--python=2.7` on the command line. 

If you're new to Python 3, the guide at may help you to get started with understanding the differences. To assist with supporting both Python 2 and 3, we have vendored the "six" package. You can read more about this and how to use it at

Note that this package depends on others that may not yet support Python 3. If these dependencies are preventing tests from passing, then we can block this bug on getting support in those packages. If there are circular dependencies then we may need to coordinate landing a sequence of patches between bugs,

Once the package supports Python 3 and the tests pass, we will also need to prepare for a new release. Bump the version number in `testing/mozbase/mozinstall/` to "2.0.0", and update the classifiers so they reflect the versions of Python that we now support.

Finally, to prepare a universal distribution, create a `testing/mozbase/mozinstall/setup.cfg` file with the following contents:


When your patch(es) are ready, you will need to push them for review. We are use MozReview for this, and instructions for how to prepare your machine and how to structure your commit messages can be found in our guide:

There may be some review issues to address, but once your contribution has been approved and subsequently landed, we will release the new version of the package!
Priority: -- → P3
Flags: sec-bounty?
Flags: in-testsuite+
Flags: in-qa-testsuite-
Flags: sec-bounty?
Flags: in-testsuite+
Flags: in-qa-testsuite-
Hello! I'd like to fix this bug , in case no one is working on this .
I did setup the build environment for Firefox, and any further mentoring would be great!
I'm going to take this one.
Assignee: nobody → wlachance
We were using more primitive methods before to support python 2.4, but
that's obviously no longer required.
Pushed by
Use subprocess check_call and check_output in mozinstall r=davehunt
Python 3 compatibility fixes in mozinstall r=davehunt
Enable and fix mozinstall tests on python 3 r=davehunt
Pushed by
Changes to support a mozinstall 2.0 release r=davehunt
No longer depends on: 1428713
See Also: → 1656225
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