Python recursive tree or fowards? Fix and simplify code

I originally was using recursion to minimax my tree from the leaves where only I have scores evaluated, but because I needed to know the depth to know whether to min or max, I switched to starting at depth=0. However, errors since sometimes currentRoot.ia = None since no score has been calculated there that deep. What I want is to keep track of depth, and find the deepest leaves that have had currentRoot.ia evaluated, and minimax from that depth at each leaf. I check if there are grandchildren since when I evaluate a position to get a score I also add a node of the move that gave that score, so there shouldn't be any scores at the leaf nodes. Scores are from the engine's point of view, so I have to negate at odd depths, although perhaps I could get away with not, if I always max the score. def minimax(currentRoot, depth): if len(currentRoot.children) > 0 and len(currentRoot.children[0].children) > 0: #There are grandchildren for child in currentRoot.children: minimax(child, depth+1) else: if depth%2 == 0: currentRoot.score = currentRoot.ia else: currentRoot.score = -currentRoot.ia return currentRoot.score measure = min if depth % 2 else max currentRoot.score = measure(c.score for c in currentRoot.children) return currentRoot.score