code: def to_header(self, span_context):
          
          trace_id = span_context.trace_id
          span_id = span_context.span_id
          trace_options = span_context.trace_options.trace_options_byte
  
          header = '{}/{};o={}'.format(
              trace_id,
              span_id,
              int(trace_options))
          return header
docs: Convert a SpanContext object to header string.
  
          :type span_context:
              :class:`~opencensus.trace.span_context.SpanContext`
          :param span_context: SpanContext object.
  
          :rtype: str
          :returns: A trace context header string in google cloud format.