Python dependency resolution — ResolutionImpossible

Log signatures

Could not find a version that satisfies the requirement
ResolutionImpossible
The conflict is caused by:
Requires-Python
No matching distribution found

What’s happening

The resolver (pip, poetry, uv) cannot find a set of versions satisfying all constraints simultaneously. The most common real causes, in order: (1) Python version mismatch — Requires-Python in the log means a pinned package version doesn't support the CI Python version (typically after a CI image bump, or a package dropping an old Python); (2) two of your dependencies pin conflicting versions of a shared transitive dependency ("The conflict is caused by:" names them — read that block, it's the whole answer); (3) a yanked release — a version you pinned was withdrawn from PyPI and fresh resolves stop finding it while cached environments still work, which is why it "works on my machine."

Fix playbook

1. 1Read the resolver's explanation block (The conflict is caused by: / ResolutionImpossible chain). Modern resolvers tell you the exact conflicting pair — believe them.
2. 2Check the Python version first: does the CI Python match what your constraints assume? A silent image bump (3.11 → 3.13) breaks resolution with zero changes on your side.
3. 3Relax or align the narrowest constraint involved in the conflict. Prefer widening your pin over forcing a transitive version.
4. 4yanked: pick the nearest non-yanked release; it was usually yanked for a reason.
5. 5Re-lock (pip-compile, poetry lock, uv lock) and rerun the exact install command from CI, with the same Python version.