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Date: Fri, 21 Feb 2014 02:48:01 +1100
Subject: Re: Commonly-used names in the Python standard library
From: Chris Angelico <rosuav@gmail.com>
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Xref: csiph.com comp.lang.python:66765

On Fri, Feb 21, 2014 at 2:14 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
>  * you won't be finding old Python versions on newer operating system
>    distributions,
>
>  * even <URL: http://www.python.org/downloads/> isn't all that extensive
>    and
>
>  * the program may import modules that were written in different Python
>    dialects.

You can always build your own Python, if it really matters... but more
likely, if you care about old versions, you actually care about *one
specific old version* which your program uses. That's why Red Hat
still supports Python 2.4 and, I think, 2.3. You can't randomly pick
up 2.2 or 1.5, but if you want 2.4, you can keep on using that for as
long as this RHEL is supported.

As to importing modules written for other versions... that can be a
major problem. Often the new keywords come with new functionality.
Take string exceptions, for instance. Say you import a module that was
written for a version that still supported them - if it raises a
string, you can't catch it. There is a limit to how far the
compatibility can be taken. Also, what happens if two modules (one of
which might be your script) written for different versions both import
some third module? Should they get different versions, based on what
version tags they use themselves? Compatibility can't be changed that
easily. You either run on the new version, or run on the old. Not
both.

ChrisA