ResolutionImpossible, duplicate requirement with contradicting Python version

[aeisenbarth]

For my project, PDM fails to resolve dependencies. I don't know whether I should do something differently, or something is wrong in the dependency, or in PDM (2.16.1):

pyproject.toml:

[project]
name = "pdm_resolve"
version = "0.1.0"
description = "Default template for PDM package"
authors = [
    {name = "Person", email = "[email protected]"},
]
dependencies = [
    "prefect~=2.16",
]
requires-python = "<3.13,>=3.9"
readme = "README.md"
license = {text = "MIT"}


[tool.pdm]
distribution = false

I did pdm install which takes very long and fails with the following log:

pdm.termui: Candidate rejected: [email protected] because it introduces a new requirement pendulum<4,>=3.0.0; python_version >= "3.12" that conflicts with other requirements:
    pendulum<3.0; python_version < "3.12" (from [email protected])
pdm.termui: Conflicts detected: 
  pendulum<3.0; python_version < "3.12" (from [email protected])
  …
  pendulum<4,>=3.0.0; python_version >= "3.12" (from [email protected])
  …
pdm.termui: Error occurs
resolvelib.resolvers.ResolutionImpossible: Unable to find a resolution

Looking at the dependency prefect shows that it lists a duplicate requirement:

pendulum < 3.0; python_version < '3.12'
pendulum >= 3.0.0, <4; python_version >= '3.12'

Apparently, this should mean, if Python < 3.12 select pendulum < 3.0, otherwise pendulum >= 3.0.0, <4. It seems PDM tries to find a way to fulfill both constraints at the same time.

• Is prefect's requirements specification correct? Does PDM support this type of constraints?
• Is there a way to avoid this with e.g. [tool.pdm.resolution.overrides]? Or do I have to constrain it to a single Python version?

[frostming]

• Is prefect's requirements specification correct? Does PDM support this type of constraints?

Correct, but PDM doesn't support this kind of constraint in a single lock result. However, you can look at lock targets, the docs include an example similar to your case.