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Date: Sat, 23 Aug 2025 08:44:14 -0600
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Subject: Re: Irritating artifacts of the python variety
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To: cygwin AT cygwin DOT com
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From: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
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Cc: Brian Inglis <Brian DOT Inglis AT SystematicSW DOT ab DOT ca>
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On 2025-08-22 19:00, Doug Henderson via Cygwin wrote:
> On Fri, Aug 22, 2025 at 10:39 AM Soren via Cygwin <cygwin AT cygwin DOT com> wrote:
>>
> 
>> ... I didn't seem to have
>> "pip" installed (notice the "seem" por favor). So I started
>> setup-x86_64 and worked through the process of installing "pip". I am
>> working with python3 so I tried to select a "pip" that corresponded
>> with it.
> 
> Python uses the "alternatives" system to allow multiple versions of
> python to be installed at the same time.
> 
> Use "man alternatives" or "info alternatives" to learn about it, as
> there are several different "alternative" implementations used by
> different *NIX systems.
> 
> Briefly, "alternatives" is located at "/usr/sbin/alternatives",
> because several of its functions required "root" or an elevated shell,
> e.g. started with "run as administrator".
> 
> The "alternatives --list" command will show you which programs are
> configured to use "alternatives". On my machine, the output looks
> like:
> 
> $ /usr/sbin/alternatives --list
> pip3                    auto    /usr/bin/pip3.12
> pydoc3                  auto    /usr/bin/pydoc3.12
> python                  manual  /usr/bin/python3.12.exe
> python3                 manual  /usr/bin/python3.12.exe
> sphinx-apidoc           auto    /usr/bin/sphinx-apidoc-3.9
> sphinx-autogen          auto    /usr/bin/sphinx-autogen-3.9
> sphinx-build            auto    /usr/bin/sphinx-build-3.9
> sphinx-quickstart       auto    /usr/bin/sphinx-quickstart-3.9
> 
> (This also shows that I have only installed the 3.9 version of the
> sphinx documentation creation suite, and not the 3.12 version.)
> 
> The "alternatives pip3" and "alternatives python3" commands show me more info:
> 
> $ /usr/sbin/alternatives --display pip3
> pip3 - status is auto.
>   link currently points to /usr/bin/pip3.12
> /usr/bin/pip3.9 - priority 39
> /usr/bin/pip3.12 - priority 312
> Current `best' version is /usr/bin/pip3.12.
> 
> $ /usr/sbin/alternatives --display python3
> python3 - status is manual.
>   link currently points to /usr/bin/python3.12.exe
> /usr/bin/python3.9 - priority 39
> /usr/bin/python3.12 - priority 312
> Current `best' version is /usr/bin/python3.12.
> 
> These show that I have two versions installed, with the 3.12 versions
> configured as the defaults. I can still run the non-default versions
> by using the full file names, e.g. "python3.9". You are strongly
> advised to use the corresponding versions together, to avoid your
> confusion and Python errors.
> 
> The root user (I, in an elevated shell) can change the default
> versions between 3.9 and 3.12 by using the interactive "alternatives
> --config python3" and "alternatives --config pip3" commands.
> 
> As a regular user, I use the "python3" or just "python" and the
> "pip3" commands to run Python and Pip. You will have to create a
> virtual environment using e.g. "python -m venv venv" to use "pip
> install" as a regular user. Otherwise you will need to run "pip
> install" in an elevated shell.

You will also find you have a bunch of postinstall (.done) and preremove scripts 
that Cygwin Setup will use to clean up your system when you (manually) select 
python2.7/3.6/3.7 for deinstall (also removing a bunch of vulnerabilities!)

$ grep alternatives /etc/postinstall/python3*.sh* /etc/preremove/python3*.sh
/etc/postinstall/python39.sh.done:/usr/sbin/alternatives --install 
/usr/bin/python python /usr/bin/python3.9 39
/etc/postinstall/python39.sh.done:/usr/sbin/alternatives --install 
/usr/bin/python3 python3 /usr/bin/python3.9 39
/etc/postinstall/python39.sh.done:/usr/sbin/alternatives --install 
/usr/bin/pydoc3 pydoc3 /usr/bin/pydoc3.9 39
/etc/postinstall/python39-devel.sh.done:/usr/sbin/alternatives --install 
/usr/bin/2to3 2to3 /usr/bin/2to3-3.9 39
/etc/postinstall/python39-devel.sh.done:/usr/sbin/alternatives --install 
/usr/bin/python3-config python3-config /usr/bin/python3.9-config 39
/etc/postinstall/python39-pip.sh.done:/usr/sbin/alternatives --install 
/usr/bin/pip3 pip3  /usr/bin/pip3.9 39
/etc/postinstall/python39-sphinx.sh.done:/usr/sbin/alternatives --install 
/usr/bin/sphinx-apidoc sphinx-apidoc /usr/bin/sphinx-apidoc-3.9 39
/etc/postinstall/python39-sphinx.sh.done:/usr/sbin/alternatives --install 
/usr/bin/sphinx-autogen sphinx-autogen /usr/bin/sphinx-autogen-3.9 39
/etc/postinstall/python39-sphinx.sh.done:/usr/sbin/alternatives --install 
/usr/bin/sphinx-build sphinx-build /usr/bin/sphinx-build-3.9 39
/etc/postinstall/python39-sphinx.sh.done:/usr/sbin/alternatives --install 
/usr/bin/sphinx-quickstart sphinx-quickstart /usr/bin/sphinx-quickstart-3.9 39
/etc/preremove/python39.sh:/usr/sbin/alternatives --remove python /usr/bin/python3.9
/etc/preremove/python39.sh:/usr/sbin/alternatives --remove python3 
/usr/bin/python3.9
/etc/preremove/python39.sh:/usr/sbin/alternatives --remove pydoc3 /usr/bin/pydoc3.9
/etc/preremove/python39-devel.sh:/usr/sbin/alternatives --remove 2to3 
/usr/bin/2to3-3.9
/etc/preremove/python39-devel.sh:/usr/sbin/alternatives --remove python3-config 
/usr/bin/python3.9-config
/etc/preremove/python39-pip.sh:/usr/sbin/alternatives --remove pip3 /usr/bin/pip3.9
/etc/preremove/python39-sphinx.sh:/usr/sbin/alternatives --remove sphinx-apidoc 
/usr/bin/sphinx-apidoc-3.9
/etc/preremove/python39-sphinx.sh:/usr/sbin/alternatives --remove sphinx-autogen 
/usr/bin/sphinx-autogen-3.9
/etc/preremove/python39-sphinx.sh:/usr/sbin/alternatives --remove sphinx-build 
/usr/bin/sphinx-build-3.9
/etc/preremove/python39-sphinx.sh:/usr/sbin/alternatives --remove 
sphinx-quickstart /usr/bin/sphinx-quickstart-3.9

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retrancher  but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

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