code: def start_span(self, name='span'):
          
          span = trace_span.BlankSpan(name, context_tracer=self)
          return span
docs: Start a span.
  
          :type name: str
          :param name: The name of the span.
  
          :rtype: :class:`~opencensus.trace.trace_span.Span`
          :returns: The Span object.