试图改变副本而不是改变原来的:(

Question

我正试图在我的 Tic Tac Toe 程序中创建一个 'smart' 对手。为此，我创建了一个 'possible win' 函数，它将决定下一回合是否有可能获胜。当运行这段代码时，我的问题是在 for 循环的每次迭代中，变量 board 似乎都被更改了。

我想在每次迭代开始时将潜在板重置为原始板，这就是我在循环开始时包含 potential_board = board[:] 的原因。然后我编辑 potential_board 但每次循环重复时这个变量都没有重置，而且板实际上也改变了。这是为什么？

非常感谢！

import random,copy

board = [['o','o',' '],[' ',' ',' '],[' ',' ',' ']]
cols = [['o',' ',' '],['o','',''],['o','','']]

def possible_win(board,player):
    """ This function should predict whether a winning move is possible in
    the next turn. This could be done by simulating every possible next move
    and running check_win() on those positions.

    :param board,player: checks a win for the specified player
    :return:
    """
    spaces = empty_spaces(board)
    print('Spaces',spaces)

    winning_moves = []

    for space in spaces:

        potential_board = board[:]

        print('PBoard',potential_board)

        print(space[0],space[1])
        potential_board[space[0]][space[1]] = 'o'

        if check_win(potential_board,'o'):
            winning_moves.append(space)




    return winning_moves


def choose_space(board):

    a = True
    while a:

        col = int(input('Choose your column of 1,2,3: ')) - 1
        row = int(input('Choose your row of 1,2,3: ')) - 1

        if board[row][col] == ' ':
            board[row][col] = 'o'
            a = False

        else: print('Sorry, try again')

    return board


def empty_spaces(board):
    empty_spaces = []
    ind = 0
    for row in board:
        ind1 = 0
        for space in row:
            if space == ' ':
                empty_spaces.append((ind, ind1))
            ind1 += 1
        ind += 1
    return empty_spaces


def comp_choose_space(board):
    choice = random.choice(empty_spaces(board))
    board[choice[0]][choice[1]] = 'x'
    return board


def check_win(board,player):

    rows = board
    columns = construct_cols(board)

    for row in board:
        # if player fills row win = True
        a = ind =  0
        for space in row:
            if rows[board.index(row)][ind] != player: break
            else: a += 1
            ind += 1
        if a == 3:
            return True

    for col in columns:
        a = ind = 0
        for space in col:
            if rows[columns.index(col)][ind] != player:
                break
            else:
                a += 1
            ind += 1
        if a == 3:
            return True

    if rows[0][0] == player and rows[1][1] == player and rows[2][2] == player \
        or rows[0][2] == player and rows[1][1] == player and rows[2][0] == player:
        return True

    return False


def construct_cols(board):
    cols = [['','',''],['','',''],['','','']]
    for row in range(len(board)):
        for col in range(row):
            cols[col][row] = board[row][col] # sounds like this should work

    return cols

def print_board(board):
    for row in board:

        print('| {} {} {} |'.format(row[0],row[1],row[2]))

def main():
    turns = 0
    board = [[' ',' ',' '],[' ',' ',' '],[' ',' ',' ']]
    print_board(board)
    win = False
    while win == False and turns < 9:
        turns += 1
        board = choose_space(board)

        if check_win(board,'o'): win,winner = True,'won'

        board = comp_choose_space(board)


        if check_win(board,'x'): win,winner = True,'lost'

        print_board(board)

    if turns == 9: print('You drew!')
    else:
        print('{}, you {}'.format('Congratulations' if winner == 'won' else 'Sorry',winner))




print(possible_win(board,'o'))
# print(empty_spaces(board))

# print(check_win(board,'o'))
# print_board(board)
# print(comp_choose_space(board))

# main()

# Future project - make the computer smarter than just randomly choosing a space
# ie seeing how close i am to winning

编辑：通过使用 copy.deepcopy() 我设法解决了这个问题，但我不明白为什么它有效而 copy.copy() 和 board[:] 无效？有人可以解释一下吗？

Answer 1

这就是 copy.deepcopy 的用途。它将遍历结构，在其中创建每个可变对象的副本。使用 slice [:] 或 shallow copy 仅复制顶层，使每行的列表共享。

基本上，如果我们从列表开始：

l = [a, b, c]

shallow = l[:]
shallow2 = copy(l)

deep = deepcopy(l)

两个shallow副本只对l进行了操作，没有对a、b或c进行操作。它们都具有 [a, b, c] 值，但是是不同的列表。他们都引用相同的 a、b 和 c 对象（从他们的角度来看，唯一的变化是引用更多）。

deep复制更深入，复制了每一个元素；它是一个形状为 [deepcopy(a), deepcopy(b), deepcopy(c)] 的新列表，无论这些值变成什么。

试图改变副本而不是改变原来的:(

Attempting to alter a copy but instead altering the original :(

python

iteration

alias

loops

pointer-aliasing