aio-libs/aiohttp · error · TypeError

data argument must be str (%r)

Error message

data argument must be str (%r)

What it means

Error "data argument must be str (%r)" thrown in aio-libs/aiohttp.

Source

Thrown at aiohttp/web_ws.py:466

    async def pong(self, message: bytes = b"") -> None:
        # unsolicited pong
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        await self._writer.send_frame(message, WSMsgType.PONG)

    async def send_frame(
        self, message: bytes, opcode: WSMsgType, compress: int | None = None
    ) -> None:
        """Send a frame over the websocket."""
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        await self._writer.send_frame(message, opcode, compress)

    async def send_str(self, data: str, compress: int | None = None) -> None:
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        if not isinstance(data, str):
            raise TypeError("data argument must be str (%r)" % type(data))
        await self._writer.send_frame(
            data.encode("utf-8"), WSMsgType.TEXT, compress=compress
        )

    async def send_bytes(self, data: bytes, compress: int | None = None) -> None:
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        if not isinstance(data, (bytes, bytearray, memoryview)):
            raise TypeError("data argument must be byte-ish (%r)" % type(data))
        await self._writer.send_frame(data, WSMsgType.BINARY, compress=compress)

    async def send_json(
        self,
        data: Any,
        compress: int | None = None,
        *,
        dumps: JSONEncoder = json.dumps,
    ) -> None:

View on GitHub (pinned to c0ef574e29)

When it happens

Trigger: Thrown at aiohttp/web_ws.py:466 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of aio-libs/aiohttp@c0ef574e29 (2026-08-04). Data as JSON: /data/errors/aa93cabc12756f71.json. Report an issue: GitHub.