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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def translate_to_trace_proto(span_data):
 """Translates the opencensus spans to ocagent proto spans. :type span_data: :class:`~opencensus.trace.span_data.SpanData` :param span_data: SpanData tuples to convert to protobuf spans :rtype: :class:`~opencensus.proto.trace.Span` :returns: Protobuf format span. """


    if not span_data:
        return None

    pb_span = trace_pb2.Span(
        name=trace_pb2.TruncatableString(value=span_data.name),
        kind=span_data.span_kind,
        trace_id=hex_str_to_bytes_str(span_data.context.trace_id),
        span_id=hex_str_to_bytes_str(span_data.span_id),
        parent_span_id=hex_str_to_bytes_str(span_data.parent_span_id)
        if span_data.parent_span_id is not None else None,
        start_time=ocagent_utils.proto_ts_from_datetime_str(
            span_data.start_time),
        end_time=ocagent_utils.proto_ts_from_datetime_str(span_data.end_time),
        status=trace_pb2.Status(
            code=span_data.status.code,
            message=span_data.status.message)
        if span_data.status is not None else None,
        same_process_as_parent_span=BoolValue(
            value=span_data.same_process_as_parent_span)
        if span_data.same_process_as_parent_span is not None
        else None,
        child_span_count=UInt32Value(value=span_data.child_span_count)
        if span_data.child_span_count is not None else None)

    # attributes
    if span_data.attributes is not None:
        for attribute_key, attribute_value \
                in span_data.attributes.items():
            add_proto_attribute_value(
                pb_span.attributes,
                attribute_key,
                attribute_value)

    # time events
    if span_data.time_events is not None:
        for span_data_event in span_data.time_events:
            if span_data_event.message_event is not None:
                pb_event = pb_span.time_events.time_event.add()
                pb_event.time.FromJsonString(span_data_event.timestamp)
                set_proto_message_event(
                    pb_event.message_event,
                    span_data_event.message_event)
            elif span_data_event.annotation is not None:
                pb_event = pb_span.time_events.time_event.add()
                pb_event.time.FromJsonString(span_data_event.timestamp)
                set_proto_annotation(
                    pb_event.annotation,
                    span_data_event.annotation)

    # links
    if span_data.links is not None:
        for link in span_data.links:
            pb_link = pb_span.links.link.add(
                trace_id=hex_str_to_bytes_str(link.trace_id),
                span_id=hex_str_to_bytes_str(link.span_id),
                type=link.type)

            if link.attributes is not None and \
                    link.attributes.attributes is not None:
                for attribute_key, attribute_value \
                        in link.attributes.attributes.items():
                    add_proto_attribute_value(
                        pb_link.attributes,
                        attribute_key,
                        attribute_value)

    # tracestate
    if span_data.context.tracestate is not None:
        for (key, value) in span_data.context.tracestate.items():
            pb_span.tracestate.entries.add(key=key, value=value)

    return pb_span