Python 2 & 3 on the same machine not so painful [LWN.net]

Python 2 & 3 on the same machine not so painful

Posted Dec 11, 2008 2:02 UTC (Thu) by leonov (subscriber, #6295)
Parent article: Python 3 is out - now what?

I may be missing something obvious here (I've taken the final release of Python as a chance to [finally!] learn a language I've heard so many good things about), but keeping multiple versions of Python around seems pretty painless:

Your library modules go into a versioned directory by default, eg.
/usr/lib/python2.5/
/usr/lib/python2.6/
/usr/lib/python3.0/

And you have a versioned executables:
/usr/bin/python2.5
/usr/bin/python2.6
/usr/bin/python3.0

Presumably you use a symlink to pick your default version:
/usr/bin/python -> /usr/bin/python2.5

Scripts written for various versions can coexist on the same machine simply by using different 'hash bang' lines:
#!/usr/bin/env python2.5
#!/usr/bin/env python2.6
#!/usr/bin/env python3.0

Of course, it would probably be a good idea for a distribution to standardise on the the same python version for all of their own scripts, but it's nice to have packages of different versions available for development and backwards compatibility purposes...

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Using it is not a big deal, packaging it is

Posted Dec 11, 2008 7:07 UTC (Thu) by khim (subscriber, #9252) [Link]

While it's true that it's trivial to use pre-packaged version of python it's not so easy to coerce python modules to play nice with few versions of Python. Installation scripts for a lot of packages out there presume /usr/bin/python is symplink to THE python you are using and refuse to support anything else. Debian copes with it, but it has the whole build infrastructure to do so: development packages will be installed removed on "as-needed" basis and as you've pointed out there are no problems with the built packages. Fedora have no such infrastructure: they just install EVERYTHING on build system and go from there. To develop such infrastructure just for python looks like an overkill to me...

Using it is not a big deal, packaging it is

Posted Dec 11, 2008 8:40 UTC (Thu) by nim-nim (subscriber, #34454) [Link]

This has not been true for many years (see mock, plague and koji). Fedora packages are built in an environment that only includes the dependencies the packages declare.

The problem is not so the plumbing or infrastructure as having people willing to package and maintain X versions of the same python modules (fighting against the upstream build scripts all the time).

It does you little good to have half your python stack one side, and half the other.

Using it is not a big deal, packaging it is

Posted Dec 11, 2008 9:53 UTC (Thu) by __alex (subscriber, #38036) [Link]

Debians "coping" with multiple Python versions is more like just ignoring the problem entirely and hoping no on will notice. easy_install-2.5 doesn't even work. This would be livable but there are hardly any modules for 2.5 in etch anyway and you end up having to install things from source constantly.