Returns all registered handlers attached to this API

def handlers(self):
        """Returns all registered handlers attached to this API"""
        used = []
        for base_url, mapping in self.routes.items():
            for url, methods in mapping.items():
                for method, versions in methods.items():
                    for version, handler in versions.items():
                        if not handler in used:
                            used.append(handler)
                            yield handler