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Groups > linux.debian.maint.python > #10704

Re: Safest way to set python3 as default for `python`

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Ben Finney wrote:
> To have a command with custom behaviour, the recommendation is the
> general one: put an executable file at ‘/usr/local/bin/python’ with
> whatever behaviour you want.

eeek, please don't! 

If a user created an incompatible /usr/local/bin/rm (didn't delete files, 
didn't exit 0), that would break a lot of tools and we'd tell the user not 
to do that. Fortunately, users don't tend to. /usr/local/bin/python is no 
different but for some reason users feel they can meddle with it.

Do not put locally versions of system tools like 'python' in root's PATH (or 
indeed in any user's PATH if the user expects to be able to run packaged 
tools). Doing so ends up potentially breaking packaged modules (they can 
find the wrong versions of dependencies in /usr/local since that is also in 
sys.path), and packaged applications (broken modules plus perhaps now 
running with the wrong version of the interpreter which is either 
incompatible or doesn't have the necessary modules installed). There's a 
reasonable number of things in /usr/bin with "#!/usr/bin/env python" that 
would be unhappy with this configuration.

We have lots of experience of this sort of breakage in #debian, where we see 
the this breaking maintainer scripts or packaged tools. As soon as we see a 
python backtrace with /usr/local in it, we know that is going to be the 
problem and expunging the local python installation from /usr/local is what 
is needed.

Putting python in other places such as /opt or ~/.local would be fine; even 
better still is to use one of the many virtualenv approaches so you're not 
even leaking that incompatible interpreter into a user's default 
environment.

(see also: please don't run pip as root)

cheers
Stuart

-- 
Stuart Prescott    http://www.nanonanonano.net/   stuart@nanonanonano.net
Debian Developer   http://www.debian.org/         stuart@debian.org
GPG fingerprint    90E2 D2C1 AD14 6A1B 7EBB 891D BBC1 7EBB 1396 F2F7

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Thread

Safest way to set python3 as default for `python` Bastian Venthur <venthur@debian.org> - 2018-07-16 09:50 +0200
  Re: Safest way to set python3 as default for `python` Matthias Klose <doko@debian.org> - 2018-07-16 13:30 +0200
    Re: Safest way to set python3 as default for `python` Bastian Venthur <venthur@debian.org> - 2018-07-16 17:20 +0200
  Re: Safest way to set python3 as default for `python` Ben Finney <bignose@debian.org> - 2018-07-18 03:40 +0200
    Re: Safest way to set python3 as default for `python` Stuart Prescott <stuart@debian.org> - 2018-07-18 11:10 +0200
      Re: Safest way to set python3 as default for `python` Brian May <bam@debian.org> - 2018-07-19 09:30 +0200
  Re: Safest way to set python3 as default for `python` Dimitri John Ledkov <xnox@ubuntu.com> - 2018-07-18 14:10 +0200

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