def join_df(left, right, left_on, right_on=None, suffix='_y'):
    """ This is a function for joining tables on specific fields. By default, we'll be doing a
    left outer join of right on the left argument using the given fields for each table.
    """
    if right_on is None:
        right_on = left_on
    return left.merge(right, how='left', left_on=left_on, right_on=right_on,
                      suffixes=("", suffix))