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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 set_stream_id(self, stream_id):
 """Set the stream id associated with this data point"""

        stream_id = validate_type(stream_id, type(None), *six.string_types)
        if stream_id is not None:
            stream_id = stream_id.lstrip('/')
        self._stream_id = stream_id