Re: [devstack][qa][python3] "also install the Python 2 dev library" - still needed?
On Mon, Sep 9, 2019 at 5:40 PM Peter Penchev pp@storpool.com wrote:
On Mon, Sep 9, 2019 at 2:55 PM Sean Mooney smooney@redhat.com wrote:
On Mon, 2019-09-09 at 11:22 +0300, 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.
yes this is a long standing issue. we discovered it a year ago but it was never fix.
in Ussrui i guess one of the first changes to devstack to make it python 3 only will be to chagne that behavior. im not sure if we will be able to change it before then.
whenever you us libs_from_git in your local.conf on a python 3 install it will install them twice both with python 2 and python 3. i hope more distros elect to symlink /usr/bin/python to python 3 some distros have chosen to do that on systems that are python only and i believe that is the correct approch.
when i encountered this it was always resuliting on the script header being #!/usr/bin/python with no version suffix i gues on a system where that points to python 3 the python 2.7 install might write python2.7 there instead?
It depends on what version of pip is invoked; I think that the way devstack invokes it nowadays it will always provide a version on the shebang line.
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)
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.
well the obvious solution is to stop doing this entirly. it was added as a hack to ensure if you use LIB_FROM_GIT in you local.conf that those libs would always be install from the git checkout that you specified in you local.conf for train we are technically requireing all project to run under python 3 so we could remove the fallback mechanium of in stalling under python 2. it was there incase a service installed under python 2 to ensure it used the same version of the lib and did not use a version form pypi instead. i wanted to stop doing this last year but we could not becase not all project could run under python 3. but now that they should be able to we dont need this hack anymore. we should change it to respec the python version you have selected. that will speed up stacking speed as we wont have to install everything twice and fix the issue you have encountered.
Yeah, thanks for confirming my thoughts that this might be the right solution. I've proposed https://review.opendev.org/681029/ (and set workflow -1) to wait for the Ussuri cycle.
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.
G'luck, Peter
Argh, I sent this from the wrong account, did I not...
G'luck, Peter
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Peter Penchev