Question on how to access a move on a line outside the main line using python-chess

Question

I'm trying to write a simple code that is capable of reading a PGN file and searching for moves and comments throughout the variant tree. However, I have not been successful, I have not yet been able to understand how I access the moves for a particular variant outside the main line.

Here is an example.

Reading the game from the pgn file below:

---

[Event "?"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "Study"]
[Black "Variant Caro-Kann"]
[Result "1/2-1/2"]
[ECO "B12"]
[Annotator "Joao Paulo"]
[PlyCount "10"]
[EventDate "2020.03.04"]
[SourceDate "2020.03.04"]

1. e4 c6 2. d4 d5 3. e5 {Variant 1} (3. exd5 {Variant 2} cxd5 4. Nf3 Nd7 (4... Nf6 {Variant 2.2} 5. c4 dxc4 6. Bxc4 e6) 5. Nc3 Ngf6) (3. Nc3 {Variant 3} dxe4 4. Nxe4 Nd7 5. Nf3 Ngf6) (3. Nd2 {Variant 4} dxe4 4. Nxe4 Nf6 5. Nxf6+ gxf6) 3... Bf5 4. Bd3 Bxd3 5. Qxd3 e6 1/2-1/2

---

Using the following code:

-------------------------------------------------------------------------- 
import chess
import chess.pgn
pgn = open("pgns/Variants Caro-Kann.pgn")
game = chess.pgn.read_game(pgn)
bd = game.board()
node = game
ct = 0;
while not node.is_end():
    print('Current Move')
    print(node.variations[0].move)
    print(node.starts_variation())
    bd.push(node.variations[0].move)
    node = node.variations[0]
    print(bd)
    print(node.starts_variation())
    print(node.comment)
    if node.is_end() == 0:
        print('Next Move')
        print(node.variations[0].move)
--------------------------------------------------------------------------
How could I access the bids for the entire variant tree (variants: 2, 2.2, 3 and 4)?
I would appreciate your help.

Answer 1

If you want to access every node, then you're basically iterating over the game tree. A straightforward recursion will get you there, something like:

def traverse(node):
    # do whatever stuff you want for the node here
    print(node.move)
    # terminating condition
    if (node.is_end()):
        return
    # recursion
    for child_node in node.variations:
        traverse(child_node)

And to use it, call traverse(game) where game is the root node of your game.