python-poetry/poetry · error · ValueError

Invalid version constraint: {constraint}

Error message

Invalid version constraint: {constraint}

What it means

ValueError from `_validate_version_constraint` (init.py:532-535) when `poetry.core.constraints.version.parse_constraint` raises. Wraps the underlying ValueError to surface the offending constraint string. Used by `poetry init` when prompting for a version constraint.

Source

Thrown at src/poetry/console/commands/init.py:535

    @staticmethod
    def _validate_package(package: str | None) -> str | None:
        if package and len(package.split()) > 2:
            raise ValueError("Invalid package definition.")

        return package

    @staticmethod
    def _validate_version_constraint(constraint: str | None) -> str | None:
        from poetry.core.constraints.version import parse_constraint

        constraint = (constraint or "").strip()
        if not constraint:
            return None

        try:
            parse_constraint(constraint)
        except ValueError as e:
            raise ValueError(f"Invalid version constraint: {constraint}") from e

        return constraint

    def _get_pool(self) -> RepositoryPool:
        from poetry.config.config import Config
        from poetry.repositories import RepositoryPool
        from poetry.repositories.pypi_repository import PyPiRepository

        if isinstance(self, EnvCommand):
            return self.poetry.pool

        if self._pool is None:
            self._pool = RepositoryPool()
            pool_size = Config.create().installer_max_workers
            self._pool.add_repository(PyPiRepository(pool_size=pool_size))

        return self._pool

View on GitHub (pinned to 92b74dcfe3)

Solutions

1. Use PEP 440 / Poetry constraint syntax: `^1.2`, `~2.0`, `>=1.0,<2.0`, `==1.4.*`.
2. Leave the prompt blank to skip the constraint.
3. Test with `python -c "from poetry.core.constraints.version import parse_constraint; parse_constraint('^1.2')"`.

Example fix

# before
~>=1.0
# after
^1.0

from poetry.core.constraints.version import parse_constraint
constraint = "^1.2"
try:
    parse_constraint(constraint)
except ValueError:
    raise SystemExit(f"invalid constraint: {constraint}")

def is_valid_constraint(value: str | None) -> bool:
    from poetry.core.constraints.version import parse_constraint
    value = (value or "").strip()
    if not value:
        return True  # blank is allowed
    try:
        parse_constraint(value)
        return True
    except ValueError:
        return False

When it happens

Trigger: Entering `>=1.0,<2` with invalid punctuation; unbalanced parentheses `(>=1.0`; unknown operators `~>=1.0`; empty constraint after stripping is allowed (returns None), so this fires only on syntactically non-empty but unparseable input.

Common situations: Mixing PEP 440 and npm-style syntax; trailing operators; copy-pasting a constraint from a non-Python ecosystem.

Related errors

• Invalid author string. Must be in the format: John Smith <jo
• Invalid package definition.
• Setting {self.argument('key')} does not exist
• You can only pass one value.
• "{value}" is an invalid value for {key}

AI-assisted analysis of python-poetry/poetry@92b74dcfe3 (2026-08-04). Data as JSON: /data/errors/b4363d620699ac70.json. Report an issue: GitHub.