[Python-Dev] Python 2.7 patch levels turning two digit

[Chris Angelico]

On Sun, Jun 22, 2014 at 2:57 AM, M.-A. Lemburg <mal at egenix.com> wrote:
> On 21.06.2014 12:51, Nick Coghlan wrote:
>> Such code has an easy fix available, though, as sys.version_info has
>> existed since 2.0, and handles two digit micro releases just fine. The
>> docs for sys.version also have this explicit disclaimer: "Do not
>> extract version information out of it, rather, use version_info and
>> the functions provided by the platform module."
>
> I don't think that's a good argument. Of course, there are
> better ways to figure out the version number, but fact is,
> existing code, even in the stdlib, does use and parse
> the sys.version string version.
>
> During Python's lifetime, we've always avoided two digit
> version numbers, so people have been relying on this, even
> if it was never (AFAIK) documented anywhere.

It's going to be a broken-code-breaking change that's introduced in a
point release, but since PEP 404 implicitly says that there won't be a
2.10.0, there's no way around that. Although actually, a glance at the
stdlib suggests that 2.10.0 (or 3.10.0) would break a lot more than
2.7.10 would break - there are places where sys.version[:3] is used
(or equivalents like "... %.3s ..." % sys.version), or a whole-string
comparison is done against a two-part version string (eg: sys.version
>= "2.6"), and at least one place that checks sys.version[0] for the
major version number, but I didn't find any that look at
sys.version[:5] or equivalent. Everything that cares about the
three-part version number seems to either look at
sys.version.split()[0] or sys.version_info. Do you know where this
problematic code is?

I checked this in the 2.7.3 stdlib as packaged on my Debian Wheezy
system, for what it's worth.

ChrisA