<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def flush(self, timeout=None, callback=None):
 """ Wait `timeout` seconds for the current events to be sent. If no `timeout` is provided, the `shutdown_timeout` option value is used. The `callback` is invoked with two arguments: the number of pending events and the configured timeout. For instance the default atexit integration will use this to render out a message on stderr. """

        if self.transport is not None:
            if timeout is None:
                timeout = self.options["shutdown_timeout"]
            self.transport.flush(timeout=timeout, callback=callback)