def date_span_intersection(date_span_1, date_span_2):
    """Return a tuple of dates representing the overlap between `date_span_1`
    and `date_span_2`.  If the date spans do not overlap, return `None`.
    """
    intersection_first_date = max(date_span_1[0], date_span_2[0])
    intersection_second_date = min(date_span_1[1], date_span_2[1])
    if intersection_first_date > intersection_second_date:
        # Date spans don't overlap
        return None
    else:
        return (intersection_first_date, intersection_second_date)