nodejs/node · error · InvalidSpecifier

Invalid specifier: '{spec}'

Error message

Invalid specifier: '{spec}'

What it means

packaging.specifiers.InvalidSpecifier raised by Specifier.__init__ when the operator+version regex finds no match in the supplied spec string. The regex expects one of the PEP 440 operator prefixes (==, !=, <=, >=, <, >, ~=, ===) followed by a version-like token; anything else is rejected before any normalization.

Source

Thrown at tools/gyp/pylib/packaging/specifiers.py:245

        "===": "arbitrary",
    }

    def __init__(self, spec: str = "", prereleases: Optional[bool] = None) -> None:
        """Initialize a Specifier instance.

        :param spec:
            The string representation of a specifier which will be parsed and
            normalized before use.
        :param prereleases:
            This tells the specifier if it should accept prerelease versions if
            applicable or not. The default of ``None`` will autodetect it from the
            given specifiers.
        :raises InvalidSpecifier:
            If the given specifier is invalid (i.e. bad syntax).
        """
        match = self._regex.search(spec)
        if not match:
            raise InvalidSpecifier(f"Invalid specifier: '{spec}'")

        self._spec: Tuple[str, str] = (
            match.group("operator").strip(),
            match.group("version").strip(),
        )

        # Store whether or not this Specifier should accept prereleases
        self._prereleases = prereleases

    # https://github.com/python/mypy/pull/13475#pullrequestreview-1079784515
    @property  # type: ignore[override]
    def prereleases(self) -> bool:
        # If there is an explicit prereleases set for this, then we'll just
        # blindly use that.
        if self._prereleases is not None:
            return self._prereleases

        # Look at all of our specifiers and determine if they are inclusive

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Use SpecifierSet for multi-constraint strings like '>=1.0,<2.0'.
2. Ensure the spec starts with a valid PEP 440 operator (==, !=, <=, >=, <, >, ~=, ===).
3. Validate or sanitize user-supplied spec strings before constructing a Specifier, catching InvalidSpecifier to report the bad input.

Example fix

# before
spec = Specifier('>=1.0,<2.0')

# after
spec = SpecifierSet('>=1.0,<2.0')

import re
_spec_re = re.compile(r'^(==|!=|<=|>=|<|>|~=|===)\s*[^\s,]+')
def is_valid_specifier(s: str) -> bool:
    return bool(_spec_re.match(s.strip()))

from packaging.specifiers import Specifier, InvalidSpecifier
def is_single_specifier(s: str) -> bool:
    try:
        Specifier(s)
        return True
    except InvalidSpecifier:
        return False

try:
    spec = Specifier(user_input)
except InvalidSpecifier as e:
    raise ValueError(f'Bad version constraint {user_input!r}: {e}') from e

When it happens

Trigger: Constructing Specifier('1.0') (missing operator), Specifier('=>1.0') (wrong operator syntax), Specifier('==1.0,<2') (compound, which belongs to SpecifierSet not Specifier), or any spec with stray whitespace/punctuation that breaks the single-spec regex.

Common situations: Passing a requirements-style specifier directly to Specifier instead of SpecifierSet, typos in version constraints, or building specifiers from unvalidated user input / config files.

Related errors

• Invalid version: '{version}'
• invalid metadata
• unparsed
• invalid or unparsed metadata
• Cannot combine SpecifierSets with True and False prerelease

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/a4cfaf953be4d51e. Report an issue: GitHub.