python-poetry/poetry · error · SolverProblemError

Because {root}, version solving failed.

Error message

Because {root}, version solving failed.

What it means

SolverProblemError is the top-level wrapper raised when the mixology version resolver cannot find any consistent assignment of package versions satisfying the full dependency graph (solver.py:185-186). It wraps a SolveFailureError and produces a root-cause message of the form 'Because {root}, version solving failed.' It signals that resolution is genuinely impossible under the current constraints, not a transient/network issue.

Source

Thrown at src/poetry/puzzle/solver.py:186

            new_packages = self._solve()
            override_packages.append((override, new_packages))

        return merge_override_packages(
            override_packages, self._package.python_constraint
        )

    def _solve(self) -> dict[Package, TransitivePackageInfo]:
        if self._provider._overrides:
            self._overrides.append(self._provider._overrides)

        try:
            result = resolve_version(self._package, self._provider)

            packages = result.packages
        except OverrideNeededError as e:
            return self._solve_in_compatibility_mode(e.overrides)
        except SolveFailureError as e:
            raise SolverProblemError(e)

        return self._aggregate_solved_packages(packages)

    def _aggregate_solved_packages(
        self, packages: list[Package]
    ) -> dict[Package, TransitivePackageInfo]:
        combined_nodes, markers = depth_first_search(
            PackageNode(self._package, packages)
        )
        results = dict(aggregate_package_nodes(nodes) for nodes in combined_nodes)
        calculate_markers(results, markers)

        # Merging feature packages with base packages
        solved_packages = {}
        for package in packages:
            if package.features:
                for _package in packages:
                    if (

View on GitHub (pinned to 92b74dcfe3)

Solutions

1. Read the full solver failure chain Poetry prints (the 'Because X, Y requires Z...' trace) to locate the root conflict.
2. Check the root python constraint in [tool.poetry.dependencies] python and the requires_python of involved packages.
3. Loosen or remove tight pins and run `poetry update` to let the solver pick compatible versions.
4. If a package was yanked/removed, switch to a maintained fork or pin an older compatible release.

Example fix

// before
[tool.poetry.dependencies]
python = "^3.8"
somelib = "^3.0"   # somelib 3.x requires python>=3.10
// after
[tool.poetry.dependencies]
python = "^3.10"
somelib = "^3.0"

from poetry.puzzle.exceptions import SolverProblemError
try:
    solved = solver.solve()
except SolverProblemError as e:
    cause = e.error  # the underlying SolveFailureError
    log.error("version solving failed: %s", cause)
    raise SystemExit(2) from e

When it happens

Trigger: Any call path into Solver.solve (poetry lock/install/update) where resolve_version raises SolveFailureError after exploring the full decision tree — e.g. the root project plus all transitive constraints have no joint solution, or python_version constraints exclude every candidate.

Common situations: python_version constraint too narrow for available releases; a dependency requires a package that was yanked/removed; conflicting pins across a large dependency tree that are not a simple pairwise conflict (so IncompatibleConstraintsError is not triggered first).

AI-assisted analysis of python-poetry/poetry@92b74dcfe3 (2026-08-04). Data as JSON: /data/errors/c84b3fb746bca7a4.json. Report an issue: GitHub.