code: def _span_attrs_to_pb(span_attr, proto_type):
      
      attr_pb = getattr(trace_pb2.Span, proto_type)()
      ParseDict(span_attr, attr_pb)
      return attr_pb
docs: Convert a span attribute dict to protobuf, including Links, Attributes,
      TimeEvents.
  
      Args:
          span_attr (dict): A dict that needs to be converted to protobuf.
          proto_type (str): The type of the Protobuf.
  
      Returns:
          An instance of the specified protobuf.