python - Return dictionary from recursive function -

i have binary search tree each node represents game length. have return dictionary key length of game , value number of games of length. recursion call goes through every node in tree returns incorrect dictionary. i'm positive problem how i'm returning dictionary. appreciated

game_len = {} if not node.children:     key = len(node.possible_next_moves())     if key not in game_len:         game_len[key] = 1     else:         game_len[key] += 1 else:     key = len(node.possible_next_moves())     if key not in game_len:         game_len[key] = 1     else:         game_len[key] += 1     [game_lengths(child) child in node.children]  return game_len 

in general, there 2 ways handle return values recursive algorithm. either can collect return values recursive calls , combine them, or can pass in mutable argument recursive calls can modify. think latter best in situation, since dictionaries easy mutate in place not easy merge together:

def game_lengths(node, result=none):     if result none:         result = {}      #... add value result dict, handle base cases, etc.      child in node.children:         game_lengths(child, result)      return result