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 deserialize(self, value):
        value = decode(value).strip()
        expanded = path.expand_path(value)
        validators.validate_required(value, self._required)
        validators.validate_required(expanded, self._required)
        if not value or expanded is None:
            return None
        return _ExpandedPath(value, expanded)