Python Mode : maximum recursion depth

Processing.py
4

Actually i’m implementing a minimax algorithm with alphabeta pruning for a chess AI but i’m getting a maximum recursive depth reached error in some positions.
I guess my recursive function minimax isn’t correct but i can’t find the problem.
Maybe you will ;p

def minimaxRoot(depth, board,isMaximizing, tour):

possibleMoves = getPossibleMoves(board, tour)
if len(possibleMoves) == 0:
    return None
bestMove = float('-inf')
bestMoveFinal = None

for m in possibleMoves:
    prev = board[m[3]][m[2]]
    board = move_test(m, board)
    value = max(bestMove, minimax(depth - 1, board,float('-inf'), float('inf'),  not isMaximizing, 1-tour))
    #affiche(board)
    board = undo(m, board, prev)
    if( value > bestMove):
        bestMove = value
        bestMoveFinal = m
return bestMoveFinal

def minimax(depth, board, a, b, is_maximizing, tour):

global nb
nb+=1
print(depth)
if(depth <1):
    return -evaluate(board, tour)

possibleMoves = getPossibleMoves(board, tour)
if len(possibleMoves) == 0:
    if isInCheck(tour,board):
        if is_maximizing:
            return float('-100000')
        else:
            return float('100000')
    else:
        if is_maximizing:
            return float('20000')
        else:
            return float('-20000')
    
#Meilleur coup pour l'ia
if(is_maximizing):
    bestMove = float('-inf')
    for m in possibleMoves:
        prev = board[m[3]][m[2]]
        board = move_test(m, board)
        bestMove = max(bestMove, minimax(depth - 1, board, a, b, not is_maximizing, 1-tour))
        board = undo(m, board, prev)
        a = max(a, bestMove)
        if b <= a:
            return bestMove
    return bestMove
#Meilleur coup de l'adversaire (= pire coup pour l'ia)
else:
    bestMove = float('inf')
    for m in possibleMoves:
        prev = board[m[3]][m[2]]
        board = move_test(m, board)
        bestMove = min(bestMove, minimax(depth - 1, board, a, b, not is_maximizing, 1-tour))
        board = undo(m, board, prev)
        b = min(b, bestMove)
        if b <= a:
            return bestMove
    return bestMove