无法弄清楚如何在此 Python 代码中重新分配列表列表中的元素

Question

我了解访问列表列表中的元素通常是如何工作的。我知道如果你有一个列表 L = [['a', 'b'], ['c', d'],['e', 'f']]，你可以使用 L[0][0] 访问 'a'。不过，我不确定为什么同样的事情在以下战舰游戏代码中不起作用：

from random import randint
from random import choice

# make a 5x5 board
board = []
row = ['O']*5
for x in range(5):
    board.append(row)

def print_board():
    for item in board:
        print ' '.join(item)

#check if input falls within 5x5 grid
def check_valid(guess_row, guess_column):
    return guess_row in range(5) and guess_column in range(5)
#return True- is valid choice, return False- not valid choice

#check that the input hasn't been guessed previously
def check_repeat(guess_row, guess_column):
    return board[guess_row][guess_column] != 'O'
#return True- repeat, reurn False- new

#check if input is a correct answer
def check_correct(guess_row, guess_column):
    return (guess_row, guess_column) == (row1, col1) or (guess_row, guess_column) == (row2, col2)
#return True- is correct, return False- is not correct

#place a 2-position ship
while True:
    #pick random place to start
    row1 = randint(0,4)
    col1 = randint(0,4)
    #choose adjacent second position
    move_direction = choice(['north', 'south', 'east', 'west'])
    if move_direction == 'north':
        row2 = row1 - 1
        col2 = col1
    elif move_direction == 'south':
        row2 = row1 + 1
        col2 = col1
    elif move_direction == 'east':
        row2 = row1
        col2 = col1 + 1
    else: # must be west 
        row2 = row1
        col2 = col1 - 1
    #check that the second position is valid, else pick new values
    if row2 in range(5) and col2 in range(5):
        break
positions_left = 2 #how many points player needs to hit
#you now have a ship at coordinates (row1, col1), (row2, col2)

turns = 5

#the gameflow itself:
print 'let\'s play battleship!'
while turns > 0:
    print 'You have %i turns remaining.' % turns
    print_board()
    guess_row = int(raw_input('Guess a row: ')) - 1 #-1 to account for python 0-indexing
    guess_column = int(raw_input('Guess a column: ')) - 1

    if check_valid(guess_row, guess_column) == False:
        print 'Sorry, those aren\'t valid coordinates'
    else: #continue game if valid
        turns -= 1
        if check_repeat(guess_row, guess_column): #old guess
            print 'You seem to have guessed that already.'
            turns += 1 #don't count this turn
        elif check_correct(guess_row, guess_column):
            print 'Hit!'
            board[guess_row][guess_column] = '!'
            positions_left -= 1
            if positions_left == 0:
                'You sunk the battleship!'
                turns = 0 #stops game
            else:
                print 'You can sink this ship in %i more hits!' % positions_left
        else:
            board[guess_row][guess_column] = 'X'
            print 'Sorry, you missed!'

问题发生在评估玩家的猜测后，我尝试将 'O' 重新分配给 '!' （表示命中）或 'X'（表示未命中）。这应该发生在：

  elif check_correct(guess_row, guess_column):
                print 'Hit!'
                board[guess_row][guess_column] = '!'

并在：

    else:
        board[guess_row][guess_column] = 'X'
        print 'Sorry, you missed!'

相反，整个列最终都被重新分配给了该值。因此，当玩家猜测第 1 行第 1 列时，该猜测被解释为 guess_row = 0, guess_column = 0。我希望 board 的新值变成：

[['X', 'O', 'O', 'O', 'O'], ['O', 'O', 'O', 'O', 'O'],['O', 'O', 'O', 'O',
'O'],['O', 'O', 'O', 'O', 'O'],['O', 'O', 'O', 'O', 'O']]

而是变成：

[['X', 'O', 'O', 'O', 'O'],['X', 'O', 'O', 'O', 'O'],['X', 'O', 'O', 'O',
'O'],['X', 'O', 'O', 'O', 'O'],['X', 'O', 'O', 'O', 'O']]

这真的很奇怪，因为当我提取一小段代码并尝试做这件事时，它工作正常，但当我尝试将其作为整个代码。

Answer 1

问题是您在每次迭代时将相同的 row 变量添加到板中。您应该添加一个新行，如下所示：

board = []
for _ in range(5):
    board.append(['O'] * 5)

Answer 2

您的问题在这里：

row = ['O']*5
for x in range(5):
    board.append(row)

由于上面的板将包含对行的 5 个引用，即相同的列表。这样改一个存，就会改所有的文件。您需要复制行，例如

for x in range(5):
    board.append(row[:])

希望对您有所帮助。

无法弄清楚如何在此 Python 代码中重新分配列表列表中的元素

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