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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _dequeue_batch(self) -> Optional[Batch]: """ Return a single batch from queue or ``None`` signaling epoch end. :raise ChildProcessError: if the enqueueing thread ended unexpectedly """

        if self._enqueueing_thread is None:
            raise ValueError('StreamWrapper `{}` with buffer of size `{}` was used outside with-resource environment.'
                             .format(self._name, self._buffer_size))
        if not self._enqueueing_thread.is_alive() and self._queue.empty():
            self._start_thread()
        while True:
            try:
                batch = self._queue.get(timeout=2)
                self._queue.task_done()
                break
            except Empty:
                if not self._enqueueing_thread.is_alive():
                    try:
                        # the enqueueing thread may just finished properly so lets check the queue eagerly
                        batch = self._queue.get_nowait()
                        self._queue.task_done()
                        break
                    except Empty:
                        # so we failed to retrieve a batch and the enqueueing thread is dead
                        # there is no hope, something must went wrong
                        raise ChildProcessError('Enqueueing thread ended unexpectedly.')
        return batch