def handler_with_header_mods(route: Route): route.fallback(headers={**route.request.headers, "FOO": "bar"})
def delete_foo_header(route: Route, request: Request): headers = request.all_headers() route.fallback(headers={**headers, "foo": None})
def handler(route: Route): try: route.fulfill(response=47) except Exception: route.fallback()