code: def start_basic_span(self, request):
          
          # noinspection PyBroadException
          try:
              # Currently Java does not populate Tracing field, so do not
              # mistaken it for a real trace ID.
              if request.tracing.trace_id:
                  context = self.tracer.extract(
                      format=ZIPKIN_SPAN_FORMAT,
                      carrier=request.tracing)
                  self.span = self.tracer.start_span(
                      operation_name=request.endpoint,
                      child_of=context,
                      tags={tags.SPAN_KIND: tags.SPAN_KIND_RPC_SERVER},
                  )
          except opentracing.UnsupportedFormatException:
              pass  # tracer might not support Zipkin format
          except:
              log.exception('Cannot extract tracing span from Trace field')
docs: Start tracing span from the protocol's `tracing` fields.
          This will only work if the `tracer` supports Zipkin-style span context.
  
          :param request: inbound request
          :type request: tchannel.tornado.request.Request