Re: Change the python interpretor to use /usr/bin/env python3

[Bernhard Voelker]

On 04/02/2018 07:53 PM, Bruno Haible wrote:
> It would make sense for the "rpm runtime dependency detection" to recognize
> the /usr/bin/env case as well. In fact, there's already a TODO item in the
> source code about this [2].
> 
> Additionally, this discussion what rpm does or does not do is not related to
> gnulib. What rpm does has an impact on the difference between a tarball/source
> code meant to be installed by users _from_source_ and a package/binaries meant
> to be installed _from_a_distro's_repositories_. This is what rpm is about.
> 
> Whereas gnulib is always installed from a tarball/source code. gnulib does not
> have distro-package maintainers.
> 
> Therefore, in gnulib, the most general solution is the best one:
>   #!/usr/bin/env python
> or
>   #!/usr/bin/env python3
> 
> The user can then create a symlink as they wish:
>   ln -s /usr/bin/python3 $HOME/bin/python
> Or rely on /etc/alternatives/...
> 
> Bruno
> 
> [2] 
> https://github.com/rpm-software-management/rpm/blob/master/scripts/script.req

Indeed, that sounded like a quirk.  Thanks for the wrap-up.

Have a nice day,
Berny

Re: Change the python interpretor to use /usr/bin/env python3

[Bruno Haible]

Darshit Shah wrote:
> On a fedora machine, Python 3 is installed by default, but not Python 2. And
> the only binary available is /usr/bin/python3.

It's not only on Fedora. The Python docs themselves ([1], footnote 1) say:

  "On Unix, the Python 3.x interpreter is by default not installed with the
   executable named 'python', so that it does not conflict with a
   simultaneously installed Python 2.x executable."

Bruno

[1] https://docs.python.org/3/tutorial/interpreter.html

Re: Change the python interpretor to use /usr/bin/env python3

[Bruno Haible]

Bernhard Voelker wrote:
> FWIW there are discussions [1] in the opposite direction, i.e., to avoid
> /usr/bin/env in the shebang where possible.  E.g. in openSUSE there is a
> check for RPM builds which leads to:
> 
>   pyrenamer.noarch: E: env-script-interpreter (Badness: 9) /usr/bin/pyrenamer 
> /usr/bin/env python
>   This script uses 'env' as an interpreter. For the rpm runtime dependency
>   detection to work, the shebang #!/usr/bin/env python  needs to be patched 
> into
>   #!/usr/bin/python  otherwise the package dependency generator merely adds a
>   dependency on /usr/bin/env rather than the actual interpreter 
> /usr/bin/python.
>   Alternatively, if the file should not be executed, then ensure that it is 
> not
>   marked as executable or don't install it in a path that is reserved for
>   executables.

It would make sense for the "rpm runtime dependency detection" to recognize
the /usr/bin/env case as well. In fact, there's already a TODO item in the
source code about this [2].

Additionally, this discussion what rpm does or does not do is not related to
gnulib. What rpm does has an impact on the difference between a tarball/source
code meant to be installed by users _from_source_ and a package/binaries meant
to be installed _from_a_distro's_repositories_. This is what rpm is about.

Whereas gnulib is always installed from a tarball/source code. gnulib does not
have distro-package maintainers.

Therefore, in gnulib, the most general solution is the best one:
  #!/usr/bin/env python
or
  #!/usr/bin/env python3

The user can then create a symlink as they wish:
  ln -s /usr/bin/python3 $HOME/bin/python
Or rely on /etc/alternatives/...

Bruno

[2] 
https://github.com/rpm-software-management/rpm/blob/master/scripts/script.req

Re: Change the python interpretor to use /usr/bin/env python3

[Bernhard Voelker]

On 04/02/2018 10:02 AM, Darshit Shah wrote:
> As you can see here, only Python 3 is installed in the base system. However,
> contrary to expectations, python3 does not provide /usr/bin/python. That 
> binary
> is provided by the `python2` package on Fedora. Since python2 is not installed
> by default in the docker container, this means that only the 
> "/usr/bin/python3"
> binary is available on that system.
> 
> However, I was mistaken about the call to `#!/usr/bin/env python` working. 
> Only
> `#!/usr/bin/env python3` works. Since Python 3 is the version that is being
> specifically targeted, could we please change it to reflect that? As far as 
> I'm
> aware, all systems with Python 3 installed always have a python3 binary
> available in $PATH. However, a /usr/bin/python may point to python 2 or 3.

FWIW there are discussions [1] in the opposite direction, i.e., to avoid
/usr/bin/env in the shebang where possible.  E.g. in openSUSE there is a
check for RPM builds which leads to:

  pyrenamer.noarch: E: env-script-interpreter (Badness: 9) /usr/bin/pyrenamer 
/usr/bin/env python
  This script uses 'env' as an interpreter. For the rpm runtime dependency
  detection to work, the shebang #!/usr/bin/env python  needs to be patched into
  #!/usr/bin/python  otherwise the package dependency generator merely adds a
  dependency on /usr/bin/env rather than the actual interpreter /usr/bin/python.
  Alternatively, if the file should not be executed, then ensure that it is not
  marked as executable or don't install it in a path that is reserved for
  executables.

[1]
https://lists.opensuse.org/opensuse-packaging/2018-03/msg00017.html

Have a nice day,
Berny



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Re: Change the python interpretor to use /usr/bin/env python3

[Darshit Shah]

Hi,

Sorry for the sparse details. I was confused the first time I saw the issue as
well, but then I forgot to mention all the details.

I was trying to test building GNU Wget2 in a Fedora 27 docker container.
So, the I am talking about Fedora 27 on x86-64. But not the full version, just
what is available in the Docker container.

> [root@075ba41dc162 /]# ls -l /usr/bin/python*
> lrwxrwxrwx 1 root root 9 Feb  8 14:46 /usr/bin/python3 -> python3.6
> -rwxr-xr-x 1 root root 11240 Feb  8 14:46 /usr/bin/python3.6
> -rwxr-xr-x 1 root root 11240 Feb  8 14:46 /usr/bin/python3.6m

> [root@075ba41dc162 /]# dnf list --installed python*
> Installed Packages
> python3.x86_64
>   3.6.4-8.fc27
> @koji-override-0
> python3-dbus.x86_64   
>   1.2.4-8.fc27
> @anaconda
> python3-dnf.noarch
>   2.7.5-2.fc27
> @koji-override-0
> python3-gpg.x86_64
>   1.9.0-6.fc27
> @anaconda
> python3-hawkey.x86_64 
>   0.11.1-1.fc27   
> @koji-override-0
> python3-iniparse.noarch   
>   0.4-26.fc27 
> @anaconda
> python3-libcomps.x86_64   
>   0.1.8-6.fc27
> @anaconda
> python3-librepo.x86_64
>   1.8.0-1.fc27
> @anaconda
> python3-libs.x86_64   
>   3.6.4-8.fc27
> @koji-override-0
> python3-pip.noarch
>   9.0.1-14.fc27   
> @koji-override-0
> python3-rpm.x86_64
>   4.14.1-1.fc27   
> @koji-override-0
> python3-setuptools.noarch 
>   37.0.0-1.fc27   
> @koji-override-0
> python3-six.noarch
>   1.11.0-1.fc27   
> @anaconda

As you can see here, only Python 3 is installed in the base system. However,
contrary to expectations, python3 does not provide /usr/bin/python. That binary
is provided by the `python2` package on Fedora. Since python2 is not installed
by default in the docker container, this means that only the "/usr/bin/python3"
binary is available on that system.

However, I was mistaken about the call to `#!/usr/bin/env python` working. Only
`#!/usr/bin/env python3` works. Since Python 3 is the version that is being
specifically targeted, could we please change it to reflect that? As far as I'm
aware, all systems with Python 3 installed always have a python3 binary
available in $PATH. However, a /usr/bin/python may point to python 2 or 3.

* Dmitry Selyutin  [180402 09:44]:
> Hello,
> 
> thank you for investigating this. I'm joining to questions asked by Paul;
> moreover, as far as I know specifying python is usually the most correct
> way to make python work regardless of version (i.e. it is supposed that one
> day there will be no distinction between python and python3).
> FWIW, the future reimplementation will drop python 2 entirely. And "python"
> branch uses /usr/bin/python too.
> 
> пн, 2 апр. 2018 г., 6:52 Paul Eggert :
> 
> > Could you please clarify this? Which Fedora release and architecture, and
> > what
> > What is the output of 'ls -l /usr/bin/python*' and of 'dnf list --installed
> > 'python*''? That sort of thing. I don't understand why '#!/usr/bin/python'
> > would
> > fail at the same time that '#!/usr/bin/env python' worked. Thanks.
> >
> >

-- 
Thanking You,
Darshit Shah
PGP Fingerprint: 7845 120B 07CB D8D6 ECE5 FF2B 2A17 43ED A91A 35B6


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Re: Change the python interpretor to use /usr/bin/env python3

[Dmitry Selyutin]

Hello,

thank you for investigating this. I'm joining to questions asked by Paul;
moreover, as far as I know specifying python is usually the most correct
way to make python work regardless of version (i.e. it is supposed that one
day there will be no distinction between python and python3).
FWIW, the future reimplementation will drop python 2 entirely. And "python"
branch uses /usr/bin/python too.

пн, 2 апр. 2018 г., 6:52 Paul Eggert :

> Could you please clarify this? Which Fedora release and architecture, and
> what
> What is the output of 'ls -l /usr/bin/python*' and of 'dnf list --installed
> 'python*''? That sort of thing. I don't understand why '#!/usr/bin/python'
> would
> fail at the same time that '#!/usr/bin/env python' worked. Thanks.
>
>

Re: Change the python interpretor to use /usr/bin/env python3

[Paul Eggert]

Could you please clarify this? Which Fedora release and architecture, and what 
What is the output of 'ls -l /usr/bin/python*' and of 'dnf list --installed 
'python*''? That sort of thing. I don't understand why '#!/usr/bin/python' would 
fail at the same time that '#!/usr/bin/env python' worked. Thanks.

Change the python interpretor to use /usr/bin/env python3

[Darshit Shah]

Hi,

On a fedora machine, Python 3 is installed by default, but not Python 2. And
the only binary available is /usr/bin/python3. This means that despite having
all the requirements to run gnulib-tool.py, one would still need to install
python to get the right binary.

However, simply changing the shebang line to `/usr/bin/env python3`, this can
be eliminated. I don't mind if you would like to keep it as `/usr/bin/env 
python` to use
the python2 interpretor by default either.

-- 
Thanking You,
Darshit Shah
PGP Fingerprint: 7845 120B 07CB D8D6 ECE5 FF2B 2A17 43ED A91A 35B6
From 3118c46aac593918441d727040c9b04ec7b2e2cc Mon Sep 17 00:00:00 2001
From: Darshit Shah 
Date: Sat, 31 Mar 2018 11:12:25 +0200
Subject: [PATCH] Use /usr/bin/env to find python interpretor

* gnulib-tool.py: Change the shebang line to "#!/usr/bin/env python3".
This way, the right python interpretor is always found irrespective of
the system. This is required since /usr/bin/python is python2 on some
machines and python3 on others
---
 gnulib-tool.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gnulib-tool.py b/gnulib-tool.py
index 32295b897..2aa5a2106 100755
--- a/gnulib-tool.py
+++ b/gnulib-tool.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2002-2018 Free Software Foundation, Inc.
 #
-- 
2.16.3



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