Calculates the lowpoints for each node in a graph.

def __get_all_lowpoints(dfs_data):
    """Calculates the lowpoints for each node in a graph."""
    lowpoint_1_lookup = {}
    lowpoint_2_lookup = {}

    ordering = dfs_data['ordering']

    for node in ordering:
        low_1, low_2 = __get_lowpoints(node, dfs_data)
        lowpoint_1_lookup[node] = low_1
        lowpoint_2_lookup[node] = low_2

    return lowpoint_1_lookup, lowpoint_2_lookup