Version numbers in Standard Library

[Thomas Jollans]

On 01/03/2019 16:35, Thompson, Matt (GSFC-610.1)[SCIENCE SYSTEMS AND
APPLICATIONS INC] via Python-list wrote:
> Dear Python List,
> 
> A question. I help maintain a Python stack for users in my division here
> at NASA and one user asked about updating the re module to 2.4. I
> believe because he read the docs:
> 
> https://docs.python.org/2.7/library/re.html
> 
> where you see lines like "New in version 2.4" and he also did:
> 
> $ python2 -c 'import re; print (re.__version__)'
> 2.2.1
> 
> And, well, one can think "oh, a newer version is needed". I searched on
> conda, etc. and can't find it and finally realized that 2.4 meant Python
> 2.4, not re 2.4. (The 3.7 docs have lines like "Changed in version 3.7".)
> 
> My question to the pros here is what purpose do the __version__/version
> variables serve in the Python Standard Library?  I can understand in
> external packages, but once in the Standard Library...?
If a module that started life outside the standard library is included
in the standard library under the same name, it is taken aboard hook,
line and sinker. If it has a __version__, then that should probably
stay: code that used the module before it entered the standard library
might rely on it.

As you quite rightly point out, these lines are then completely
pointless, so there's no reason to ever change them.

> 
> For example, in re.py, that line was last changed 18 years ago according
> to git blame. In tarfile.py, the version string was last changed 12
> years ago. But in both, the modules were edited in 2018 so they haven't
> been static for a decade.
> 
> Are those strings there just for historic purposes?
> 
> Not a big deal, I was just wondering.
> 
> Thanks,
> Matt
>