python/cpython · error · TypeError

executor must be ThreadPoolExecutor instance

Error message

executor must be ThreadPoolExecutor instance

What it means

Error "executor must be ThreadPoolExecutor instance" thrown in python/cpython.

Source

Thrown at Lib/asyncio/base_events.py:908

    def run_in_executor(self, executor, func, *args):
        self._check_closed()
        if self._debug:
            self._check_callback(func, 'run_in_executor')
        if executor is None:
            executor = self._default_executor
            # Only check when the default executor is being used
            self._check_default_executor()
            if executor is None:
                executor = concurrent.futures.ThreadPoolExecutor(
                    thread_name_prefix='asyncio'
                )
                self._default_executor = executor
        return futures.wrap_future(
            executor.submit(func, *args), loop=self)

    def set_default_executor(self, executor):
        if not isinstance(executor, concurrent.futures.ThreadPoolExecutor):
            raise TypeError('executor must be ThreadPoolExecutor instance')
        self._default_executor = executor

    def _getaddrinfo_debug(self, host, port, family, type, proto, flags):
        msg = [f"{host}:{port!r}"]
        if family:
            msg.append(f'family={family!r}')
        if type:
            msg.append(f'type={type!r}')
        if proto:
            msg.append(f'proto={proto!r}')
        if flags:
            msg.append(f'flags={flags!r}')
        msg = ', '.join(msg)
        logger.debug('Get address info %s', msg)

        t0 = self.time()
        addrinfo = socket.getaddrinfo(host, port, family, type, proto, flags)
        dt = self.time() - t0

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Pass a concurrent.futures.ThreadPoolExecutor instance to loop.set_default_executor(); ProcessPoolExecutor is not supported as the default executor.

When it happens

Trigger: Raised when set_default_executor() is given an executor that is not a ThreadPoolExecutor.

Common situations: See trigger scenarios.

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/2f464181663a534c. Report an issue: GitHub.