def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def _invert_results(self, candidates):
        inverted_candidates = list(self.directory)

        for candidate in candidates:
            try:
                inverted_candidates.remove(candidate)
            except ValueError:
                pass

        return inverted_candidates