On Mon, Sep 9, 2019, at 1:22 AM, Peter Penchev wrote:
Hi,
When devstack's `setup_dev_lib` function is invoked and USE_PYTHON3 has been specified, this function tries to also install the development library for Python 2.x, I guess just in case some package has not declared proper Python 3 support or something. It then proceeds to install the Python 3 version of the library and all its dependencies.
Unfortunately there is a problem with that, and specifically with script files installed in the system's executable files directory, e.g. /usr/local/bin. The problem appears when some Python library has already been installed for Python 3 (and has installed its script files), but is now installed for Python 2 (overwriting the script files) and is then not forcefully reinstalled for Python 3, since it is already present. Thus, the script files are last modified by the Python 2 library installation and they have a hashbang line saying `python2.x` - so if something then tries to execute them, they will run and use modules and libraries for Python 2 only.
We experienced this problem when running the cinderlib tests from Cinder's `playbooks/cinderlib-run.yaml` file - it finds a unit2 executable (installed by the unittest2 library) and runs it, hoping that unit2 will be able to discover and collect the cinderlib tests and load the cinderlib modules. However, since unittest2 has last been installed as a Python 2 library, unit2 runs with Python 2 and fails to locate the cinderlib modules. (Yes, we know that there are other ways to run the cinderlib tests; this message is about the problem exposed by this way of running them)
One option here is to explicitly run the file under the python version you want. I do this with `pbr freeze` frequently to ensure I'm looking at the correct version of software for the correct version of python. For example: python3 /usr/local/bin/pbr freeze | grep $packagename python2 /usr/local/bin/pbr freeze | grep $packagename Then as long as you have installed the utility (in my case pbr) under both python versions it should just work assuming they don't write different files for different versions of python at install time.
The obvious solution would be to instruct the Python 2 pip to not install script (or other shared) files at all; unfortunately, https://github.com/pypa/pip/issues/3980 ("Option to exclude scripts on install"), detailing a very similar use case ("need it installed for Python 2, but want to use it with Python 3") has been open for almost exactly three years now with no progress. I wonder if I could try to help, but even if this issue is resolved, there will be some time before OpenStack can actually depend on a recent enough version of pip.
Note OpenStack tests with, and as a result possibly requires, the latest version of pip. Fixing this in pip shouldn't be a problem as long as they make a release not long after.
A horrible workaround would be to find the binary directory before installing the Python 2 library (using something like `pip3.7 show somepackage` and then running some heuristics on the "Location" field), tar'ing it up and then restoring it... but I don't know if I even want to think about this.
Another possible way forward would be to consider whether we still want the Python 2 libraries installed - is OpenStack's Python 3 transition reached a far enough stage to assume that any projects that still require Python 2 *and* fail to declare their Python 2 dependencies properly are buggy? To be honest, this seems the most reasonable path for me - drop the "also install the Python 2 libs" code and see what happens. I could try to make this change in a couple of test runs in our third-party Cinder CI system and see if something breaks.
snip Hope this helps, Clark