code: def get_span(self, request=None):
          
          if request is None and stack.top:
              request = stack.top.request
  
          scope = self._current_scopes.get(request, None)
          return None if scope is None else scope.span
docs: Returns the span tracing `request`, or the current request if
          `request==None`.
  
          If there is no such span, get_span returns None.
  
          @param request the request to get the span from