python/cpython · error · TypeError

delay must not be None

Error message

delay must not be None

What it means

Error "delay must not be None" thrown in python/cpython.

Source

Thrown at Lib/asyncio/base_events.py:798

    def call_later(self, delay, callback, *args, context=None):
        """Arrange for a callback to be called at a given time.

        Return a Handle: an opaque object with a cancel() method that
        can be used to cancel the call.

        The delay can be an int or float, expressed in seconds.  It is
        always relative to the current time.

        Each callback will be called exactly once.  If two callbacks
        are scheduled for exactly the same time, it is undefined which
        will be called first.

        Any positional arguments after the callback will be passed to
        the callback when it is called.
        """
        if delay is None:
            raise TypeError('delay must not be None')
        timer = self.call_at(self.time() + delay, callback, *args,
                             context=context)
        if timer._source_traceback:
            del timer._source_traceback[-1]
        return timer

    def call_at(self, when, callback, *args, context=None):
        """Like call_later(), but uses an absolute time.

        Absolute time corresponds to the event loop's time() method.
        """
        if when is None:
            raise TypeError("when cannot be None")
        self._check_closed()
        if self._debug:
            self._check_thread()
            self._check_callback(callback, 'call_at')
        timer = events.TimerHandle(when, callback, args, self, context)

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Pass a numeric delay (seconds) to loop.call_later(delay, callback); use 0 to schedule as soon as possible instead of None.

When it happens

Trigger: Raised when call_later() is invoked with delay=None.

Common situations: See trigger scenarios.

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/0a0f6a02358a8746. Report an issue: GitHub.