CODEWITHSUNDEEP
pythonalgorithmartificial-intelligencegame-developmentminimax
freddy kruger
freddy kruger

Reputation: 35

minimax algorithm resulting a recursion error

I'm trying to implement this turn-based "Fighting game" using a minimax algorithm. However, I ran into some problems. THe code worked the first time running it but after running it the second time It gave an error.

I thought applying alpha-beta pruning would solve the issue but it's still the same.

RecursionError: maximum recursion depth exceeded while calling a Python object.

This is the minimax algorithm that's causing the error

def minimax(self, depth, is_maximizing, alpha, beta):
    if depth == 0 or self.is_winning(self.computer) or self.is_winning(self.player) or self.is_draw():
        if self.is_winning(self.computer):
            return self.computer_score - depth
        if self.is_winning(self.player):
            return -self.player_score + depth
        if self.is_draw():
            return 0

    if is_maximizing:
        best_value = float('-inf')
        for move in ["slash", "thrust"]:
            self.attack = move
            value = self.minimax(depth - 1, False, alpha, beta)
            best_value = max(best_value, value)
            alpha = max(alpha, best_value)
            if beta <= alpha:
                break
        return best_value
    else:
        best_value = float('inf')
        for move in ["block", "dodge"]:
            self.defend = move
            value = self.minimax(depth - 1, True, alpha, beta)
            best_value = min(best_value, value)
            beta = min(beta, best_value)
            if beta <= alpha:
                break
        return best_value

What am I missing here? Any answer that's helpful is appreciated.

Upvotes: 1

Views: 187

Answers (1)

Steggy
Steggy

Reputation: 76

The problem is here:

if depth == 0 or self.is_winning(self.computer) or self.is_winning(self.player) or self.is_draw():
    if self.is_winning(self.computer):
        return self.computer_score - depth
    if self.is_winning(self.player):
        return -self.player_score + depth
    if self.is_draw():
        return 0

There is no default condition, so it is possible for your minmax function to go to past depth=0. You can fix this easily by adding a return at the end.

if depth == 0 or self.is_winning(self.computer) or self.is_winning(self.player) or self.is_draw():
    if self.is_winning(self.computer):
        return self.computer_score - depth
    if self.is_winning(self.player):
        return -self.player_score + depth
    if self.is_draw():
        return 0
    return 0 # Or replace with an evaluation function

Upvotes: 2

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