: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

def emit(self, span_datas):
        """
        :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
        """
        envelopes = [self.span_data_to_envelope(sd) for sd in span_datas]
        result = self._transmit(envelopes)
        if result > 0:
            self.storage.put(envelopes, result)