For what it’s worth: I have been following the Python packaging topics on Stack Overflow for a bit now, and I can’t remember people having issues with the PEP 508/PEP 440 notations themselves. The cases I remember where about people being confused about which notation to use because of the deprecation of setuptools dependency_links (that was a bit rough). Once pointed to the right document, people seemed to be satisfied (or at least they went quiet). And I haven’t seen such a question in months (of course I haven’t seen every question).
A wider, more public poll would be welcome.
For the simple cases (which might be the most common cases: just the name, plus sometimes a pinned version or a range), PEP 508 feels more readable to me. My gut feeling is that when people need more than that, then they are somewhat experienced enough that they don’t get scared by such notation. A pleasant user experience is important, but we are talking about people who at the very least managed to write the very Python code they are trying to package, so I believe it’s not a big ask.
But obviously I would feel bad, if poetry (and others) had to give up on their notation. I would vote for a reasonable hybrid notation (I think there were some suggestions here), but I am aware it would make for more complex specification and implementations. I would encourage the proponents of a TOML notation to come up with more suggestions.
Maybe something like that:
dependencies = [
'A [one, two] ~= 1.2.3 ; python_version < "2.7"',
{ name = 'B [one, two] ~= 1.2.3 ; python_version < "2.7"' },
{ name = 'C [one, two] ~= 1.2.3', markers = 'python_version < "2.7"' },
{ name = 'D [one, two]', version = '~= 1.2.3', markers = 'python_version < "2.7"' },
{ name = 'E', extras = [ 'one', 'two' ], version = '~= 1.2.3', markers = 'python_version < "2.7"' },
]
Basically parse name as PEP 508 first and then everything that comes after replaces (no questions asked, conflicts are user’s fault) what’s already in the Requirement object. I believe it’s quite close to poetry’s notation.