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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 _extract_annotations_from_span(span):
 """Extract and convert time event annotations to zipkin annotations"""

    if span.time_events is None:
        return []

    annotations = []
    for time_event in span.time_events:
        annotation = time_event.annotation
        if not annotation:
            continue

        event_timestamp_mus = timestamp_to_microseconds(time_event.timestamp)
        annotations.append({'timestamp': int(round(event_timestamp_mus)),
                            'value': annotation.description})

    return annotations