def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def __setattr__(self, name: str, value: Any):
        """Custom __setattr__ to allow access to metrics schema fields."""

        if not self._initialized:
            object.__setattr__(self, name, value)
            return

        if name not in self._metric_fields:
            raise RuntimeError(
                'Field: {} not defined in metirc schema'.format(name))

        self._values[name] = value