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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 halt(self, checkpoint=None, finished=False, raise_error=True):
 """ Stop the pipeline before completion point. :param str checkpoint: Name of stage just reached or just completed. :param bool finished: Whether the indicated stage was just finished (True), or just reached (False) :param bool raise_error: Whether to raise an exception to truly halt execution. """

        self.stop_pipeline(PAUSE_FLAG)
        self._active = False
        if raise_error:
            raise PipelineHalt(checkpoint, finished)