Wrapper for sgf files, returning go.PositionWithContext instances.

    It does NOT return the very final position, as there is no follow up.
    To get the final position, call pwc.position.play_move(pwc.next_move)
    on the last PositionWithContext returned.

    Example usage:
    with open(filename) as f:
        for position_w_context in replay_sgf(f.read()):
            print(position_w_context.position)

def replay_sgf(sgf_contents):
    """Wrapper for sgf files, returning go.PositionWithContext instances.

    It does NOT return the very final position, as there is no follow up.
    To get the final position, call pwc.position.play_move(pwc.next_move)
    on the last PositionWithContext returned.

    Example usage:
    with open(filename) as f:
        for position_w_context in replay_sgf(f.read()):
            print(position_w_context.position)
    """
    root_node = get_sgf_root_node(sgf_contents)
    props = root_node.properties
    assert int(sgf_prop(props.get('GM', ['1']))) == 1, "Not a Go SGF!"

    komi = 0
    if props.get('KM') is not None:
        komi = float(sgf_prop(props.get('KM')))
    result = utils.parse_game_result(sgf_prop(props.get('RE', '')))

    pos = Position(komi=komi)
    current_node = root_node
    while pos is not None and current_node.next is not None:
        pos = handle_node(pos, current_node)
        maybe_correct_next(pos, current_node.next)
        next_move = get_next_move(current_node)
        yield PositionWithContext(pos, next_move, result)
        current_node = current_node.next