code: def emit(self, span_datas):
          
          envelopes = [self.span_data_to_envelope(sd) for sd in span_datas]
          result = self._transmit(envelopes)
          if result > 0:
              self.storage.put(envelopes, result)
docs: :type span_datas: list of :class:
              `~opencensus.trace.span_data.SpanData`
          :param list of opencensus.trace.span_data.SpanData span_datas:
              SpanData tuples to emit