[Catalog-sig] Finalising PEP-345 - Requires-Python

[David Lyon]

> Requires-Python
>
> This field specifies the Python version(s) that the package is 
> guaranteed to be compatible with.
>
> Version numbers must be in the format specified in Version Specifiers.
>
> Examples:
> 
> Requires-Python: 2.5
> Requires-Python: >2.1
> Requires-Python: >=2.3.4
> Requires-Python: >=2.5,<2.7

I think most untrained readers, would find the ">=2.5,<2.7" notation
to be non-obvious and ambiguous.

The shortest known method to express the condition is 
"Requires-Python: 2.5:2.7"

Most importantly, specifying a logical 'AND' operation with a comma is 
obscure and verbose. We don't find any prior examples in any programming
language that I know of where comma's are used to denote a logical 
'and' operation.

What it seems to imply is that there is a pipeline of logical
expressions built into a comma seperated list. That must be
parsed, and if all are true, then the condition is accepted.

I think it would take me some time if I had to explain this proposed
solution to a computer sciences teacher in an exam situation. I
don't think I'd be so confident of getting a pass.

It would be way more logical to do the and operation by
specifying multiple conditions.

  Requires-Python: >=2.5
  Requires-Python: <2.7

As there is an implication that the file will be parsed
sequentially, and every conditional line needs to process
with a true result.

Still, the shortest known way is "Requires-Python: 2.5:2.7"

David