Marker class final

Marker

python source

class Marker:
    def __init__(self, marker: str) -> None:
        # Note: We create a Marker object without calling this constructor in
        #       packaging.requirements.Requirement. If any additional logic is
        #       added here, make sure to mirror/adapt Requirement.
        try:
            self._markers = _normalize_extra_values(_parse_marker(marker))
            # The attribute `_markers` can be described in terms of a recursive type:
            # MarkerList = List[Union[Tuple[Node, ...], str, MarkerList]]
            #
            # For example, the following expression:
            # python_version > "3.6" or (python_version == "3.6" and os_name == "unix")
            #
            # is parsed into:
            # [
            #     (<Variable('python_version')>, <Op('>')>, <Value('3.6')>),
            #     'and',
            #     [
            #         (<Variable('python_version')>, <Op('==')>, <Value('3.6')>),
            #         'or',
            #         (<Variable('os_name')>, <Op('==')>, <Value('unix')>)
            #     ]
            # ]
        except ParserSyntaxError as e:
            raise InvalidMarker(str(e)) from e

    def __str__(self) -> str:
        return _format_marker(self._markers)

    def __repr__(self) -> str:
        return f"<Marker('{self}')>"

    def __hash__(self) -> int:
        return hash((self.__class__.__name__, str(self)))

    def __eq__(self, other: Any) -> bool:
        if not isinstance(other, Marker):
            return NotImplemented

        return str(self) == str(other)

    def evaluate(self, environment: Optional[Dict[str, str]] = None) -> bool:
        """Evaluate a marker.

        Return the boolean from evaluating the given marker against the
        environment. environment is an optional argument to override all or
        part of the determined environment.

        The environment is determined from the current Python process.
        """
        current_environment = default_environment()
        current_environment["extra"] = ""
        if environment is not None:
            current_environment.update(environment)
            # The API used to allow setting extra to None. We need to handle this
            # case for backwards compatibility.
            if current_environment["extra"] is None:
                current_environment["extra"] = ""

        return _evaluate_markers(self._markers, current_environment)