def __init__(self, groups=None):
        super(GroupedRequirements, self).__init__(NamedRequirements)
        self.groups = groups or self.default_groups
        self.filename = None
        self.create_default_groups()
def rel(self, f):
        """Convert repo path back to path that is relative to cwd of matcher."""
        return util.pathto(self._root, self._cwd, f)