[Python-ideas] Specifying Python version

[Cameron Simpson]

On 17May2018 10:33, Steven D'Aprano <steve at pearwood.info> wrote:
>On Wed, May 16, 2018 at 08:02:47PM +0100, MRAB wrote:
>> Instead of verbatim identifiers, how about a special comment giving the
>> Python version in which the file was written?
>>
>> There could then be a tool similar to 2to3 that converts the file to a
>> more recent version of Python that might have new reserved words. In
>> most cases the new file would merely be a copy of the original, but with
>> an updated Python version.
>
>That would be a serious PITA for modules which have to work with more
>than one version of Python.

It also feels rather fragile. Though I'm having a little trouble formulating a 
concrete example, I just feel like this is the kind of thing that is easily 
mangled.

For example in a revision control merge (pull new change from branch using 
older Python, whose older Python got slightly changed in the special comment - 
in the diff the special comment looks new, easy to accidentally roll over the 
target branch whose special comment has been updated:

  main branch: # ##pyver 3.3##
  maintenance branch:  # ##pyver 2.4##
  maintenance branch:  update to # ##pyver 2.5## and add a feature or fix
  main branch: merge changeset from maintenance, tread on the "3.3" with "2.5"

Cheers,
Cameron Simpson <cs at cskk.id.au>