Re: [dpdk-dev] [PATCH 0/9] python2 deprecation notice

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Jul 10, 2020 at 03:33:58PM +0200, Robin Jarry wrote:
> Hi Louise,
> 
> 2020-07-10, Louise Kilheeney:
> > This patchset adds deprecation notices to python scripts,
> > warning of the removal of python2 support from the DPDK 20.11 release.
> 
> While showing warnings to users about Python 2 support drop in 20.11 is
> good, it seems like the shebangs in a lot of these scripts still refer
> to "python".
> 
> dpdk$ git describe 
> v20.05-623-geff30b59cc2e
> dpdk$ git grep '#.*!.*python\>'
> app/test-bbdev/test-bbdev.py:1:#!/usr/bin/env python
> app/test-cmdline/cmdline_test.py:1:#!/usr/bin/env python
> app/test/autotest.py:1:#!/usr/bin/env python
> buildtools/map_to_win.py:1:#!/usr/bin/env python
> config/arm/armv8_machine.py:1:#!/usr/bin/python
> devtools/update_version_map_abi.py:1:#!/usr/bin/env python
> usertools/cpu_layout.py:1:#!/usr/bin/env python
> usertools/dpdk-devbind.py:1:#! /usr/bin/env python
> usertools/dpdk-pmdinfo.py:1:#!/usr/bin/env python
> usertools/dpdk-telemetry-client.py:1:#! /usr/bin/env python
> 
> On many distros, "python" still points (as of today) to python2. You
> series will cause warnings that cannot be avoided.
> 
> Also, on some distros, "python" does not exist at all (RHEL 8 and CentOS
> 8 for example). And only "python2" or "python3" are available.
> 
> I wonder if it would not be better to find a way to make these shebangs
> "dynamic" somehow. It is not trivial and I don't see any other solution
> than plain modification of the shebangs at build time.
> 
> However, there is no way (to my knowledge) to specify which version of
> python is "selected" during the build.
> 
> Does anyone have a proper solution?
> 
That's a good point and I'm not sure there is a clean solution to it -
especially if there is no "python" without a 2 or 3 at the end?

Theoretically we could put something like this at the start of each script
to ensure it runs with python3 if available and "python" otherwise:

from __future__ import print_function
import sys
import os
import distutils.spawn

if sys.version_info.major < 3:
    py3 = distutils.spawn.find_executable("python3")
    if py3:
        print("Running", ' '.join([py3] + sys.argv))
        sys.exit(os.system(' '.join([py3] + sys.argv)))

print("Running", str(sys.argv), "with python version",\
    str(sys.version_info.major) + "." + str(sys.version_info.minor))

It doesn't solve the problem of those systems where /usr/bin/env python
returns nothing, but in those cases the script won't run at all, so the
user needs to explicitly call via python2/3 directly and the deprecation
notice is correct if they pick the wrong one. For most distros where
"python" alone does exist, the above code will work to prevent the
deprecation notice appearing except where the user does not have python3
available.

If we want to go with a build-time selection approach, we should just
change the defaults in all scripts to python3 and only change them back in
the Makefile build if python3 is not found. [Meson requires python3, so we
can ignore any checks there.]

Regards,
/Bruce