python-poetry/poetry · error · ValueError

Could not find a matching version of package {name}

Error message

Could not find a matching version of package {name}

What it means

ValueError from `_find_best_version_for_package` (init.py:455-457) when `VersionSelector.find_best_candidate` returns None — no package on the configured pool matches the name (and constraint). Used by `poetry init` / `poetry add` interactive flows to validate a requested dependency.

Source

Thrown at src/poetry/console/commands/init.py:457

        return result

    def _find_best_version_for_package(
        self,
        name: str,
        required_version: str | None = None,
        allow_prereleases: bool | None = None,
        source: str | None = None,
    ) -> tuple[str, str]:
        from poetry.version.version_selector import VersionSelector

        selector = VersionSelector(self._get_pool())
        package = selector.find_best_candidate(
            name, required_version, allow_prereleases=allow_prereleases, source=source
        )

        if not package:
            # TODO: find similar
            raise ValueError(f"Could not find a matching version of package {name}")

        version = package.version.without_local()
        return package.pretty_name, f"^{version.to_string()}"

    def _parse_requirements(self, requirements: list[str]) -> list[dict[str, Any]]:
        from poetry.core.pyproject.exceptions import PyProjectError

        try:
            cwd = self.poetry.file.path.parent
            artifact_cache = self.poetry.pool.artifact_cache
        except (PyProjectError, RuntimeError):
            cwd = Path.cwd()
            artifact_cache = self._get_pool().artifact_cache

        parser = RequirementsParser(
            artifact_cache=artifact_cache,
            env=self.env if isinstance(self, EnvCommand) else None,
            cwd=cwd,

View on GitHub (pinned to 92b74dcfe3)

Solutions

1. Verify the name on the registry (PyPI or configured source) and correct typos.
2. Add the source: `poetry source add <name> <url>` then retry.
3. Loosen or fix the version constraint; pass `--allow-prereleases` if only pre-releases exist.
4. Check network/proxy reachability of the index URL.

Example fix

# before
poetry add requets
# after
poetry add requests

from poetry.repositories.pypi_repository import PyPiRepository
repo = PyPiRepository(config=...)
packages = repo.search("requests")  # or repo.package(name, version)
if not packages:
    raise SystemExit("package not found on the configured pool")

def package_exists(pool, name: str, constraint: str | None = None) -> bool:
    from poetry.version.version_selector import VersionSelector
    selector = VersionSelector(pool)
    return selector.find_best_candidate(name, constraint) is not None

try:
    name, version = cmd._find_best_version_for_package(name, constraint)
except ValueError:
    # correct name, add source, or loosen constraint
    ...

When it happens

Trigger: Typoed package name; package exists only on a source not in the pool; required version constraint excludes every published release; prereleases exist but `allow-prereleases` is false.

Common situations: Private index not configured; package renamed or yanked; pin like `>=2` when only `1.x` is published; network/proxy blocking the registry.

Related errors

• Invalid package definition.
• The following packages were not found: {', '.join(sorted(not
• Failed to install required Poetry plugins
• Redirects are not supported. Is the URL missing a trailing s
• HTTP Error {e.response.status_code}: {e.response.reason} | {

AI-assisted analysis of python-poetry/poetry@92b74dcfe3 (2026-08-04). Data as JSON: /data/errors/8f13d2b7f72cecbb.json. Report an issue: GitHub.