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 visitdir(self, dir):
        dir = normalizerootdir(dir, "visitdir")
        if not self._m2.visitdir(dir):
            return self._m1.visitdir(dir)

        if self._m2.visitdir(dir) == "all":
            # There's a bug here: If m1 matches file 'dir/file' and m2 excludes
            # 'dir' (recursively), we should still visit 'dir' due to the
            # exception we have for exact matches.
            return False
        return bool(self._m1.visitdir(dir))