Poetry & PEP440 Disagree on an example in the PEP.

[r-richmond]

• Poetry version: 1.2.2
• Python version: 3.10.8
• OS version and name: macOS 13.0.1
• pyproject.toml: N/A

• I am on the latest stable Poetry version, installed using a recommended method.
• I have searched the issues of this repo and believe that this is not a duplicate.
• I have consulted the FAQ and blog for any relevant entries or release notes.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option) and have included the output below.

Issue

Discovered during the conversation in #7047.

Poetry does not return the same results as one of the examples in PEP 440.

#!/usr/bin/env python3

from poetry.core.constraints.version.version import Version
from poetry.core.constraints.version import parse_constraint

constraint = parse_constraint("==1.1.*")
version = Version.parse("1.1a1")
allowed = constraint.allows(version)
print(f"{allowed=}")

prints allowed=False which does not match the example here

cc: @dimbleby

[dimbleby]

Currently ==1.1.* is parsed as >=1.1.0,<1.2

A possible approach for a fix would be to instead recognise this as >=1.1.0.dev0,<1.2.

[radoering]

A possible approach for a fix would be to instead recognise this as >=1.1.0.dev0,<1.2.

Please be aware that this is probably not sufficient and will result in other issues. cf python-poetry/poetry-core#402 (review)

IMO we have to change our "implicitly allow pre-releases" logic because our "allow pre-releases" is more like "do not prefer stable releases".

[dimbleby]

probably "allow-prereleases" on individual dependencies was a mistake.

• It doesn't help at all to describe the desired behaviour for transitive dependencies
• People quite often seem to be confused by it, expecting eg that { version = ">=1.3.0", allow-prereleases = true } should allow 1.3.0 pre-releases.
  • That's not poetry's behaviour (and my reading of PEP440 is that poetry is correct)

The default behaviour at https://peps.python.org/pep-0440/#handling-of-pre-releases requires no special flag and should be quite satisfactory.

Poetry currently fails to satisfy the "tools ... SHOULD" section which is about explicitly allowing or disallowing pre-releases for all distributions (eg including transitive dependencies)

Poetry is doing a half-assed job of the "tools ... MAY" section about doing the same on a per-distribution basis. (Because this is not configurable for transitive dependencies.)

Obvs removing this flag would require some consensus and deprecation period, but simplification is a noble goal...

[github-actions]

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