Python 列表索引超出范围，但我尝试调试它，我可以'；我没有发现任何错误

我正在制作一个N皇后算法（八皇后难题是将八个国际象棋皇后放在一个8×8的棋盘上，这样就不会有两个皇后相互威胁；因此，解决方案要求两个皇后不共享同一行、列或对角线），这是“外部”，而不是算法： 但是它给了我一个错误（在巨大的代码后面列出），我打印了每一个东西，5在8之内

a = [0, 0, 0, 0, 0, 0, 0, 0]
b = [0, 0, 0, 0, 0, 0, 0, 0]
c = [0, 0, 0, 0, 0, 0, 0, 0]
d = [0, 0, 0, 0, 0, 0, 0, 0]
e = [0, 0, 0, 0, 0, 0, 0, 0]
f = [0, 0, 0, 0, 0, 0, 0, 0]
g = [0, 0, 0, 0, 0, 0, 0, 0]
h = [0, 0, 0, 0, 0, 0, 0, 0]

board = [a,b,c,d,e,f,g,h]
for row in board:
    for elem in row:
        print(elem, end=' ')
    print()

#ask for first queen position

firstq_x = int(input('What is x of first queen: '))
print(firstq_x)
firstq_y = int(input('What is y of first queen: '))
print(firstq_y)
#board[firstq_y] and board[firstq_y[firstq_x]]

y = board[int(firstq_y)-1] # y is the selection of a,b,c,d,e,f,g, or h.
y[int(firstq_x)-1] = 'Q' # y[int(firstq_x)-1] is the selection of 0's based on y.

for row in board:
    for elem in row:
        print(elem, end=' ')
    print()

#horizontal
for floor in range(8):
    if y[floor] == 0:
        y[floor] = "X"
        
#vertical
board = [a,b,c,d,e,f,g,h]

count = 0

for vert in range(len(board)):
    vertical = board[count]
    if vertical[firstq_x-1] == 0:
        vertical[firstq_x-1] = "X"
    count+=1
    
#NW
#find y first
ytofill = 2
yminus1 = board[firstq_y-ytofill]  #this will give us list before current list
#find x next
xtofill = 1
xminus1 = yminus1[firstq_x-xtofill]  #this will give us letter before letter
#execute

if firstq_y>firstq_x:

    for NW in range(firstq_x):
        if yminus1[firstq_x-xtofill] == 0:
            yminus1[firstq_x-xtofill] = 'X'
        yminus1 = board[firstq_y-ytofill]
        xtofill+=1
        ytofill+=1

else:
    
    for NW in range(firstq_y):
        if yminus1[firstq_x-xtofill] == 0:
            yminus1[firstq_x-xtofill] = 'X'
        yminus1 = board[firstq_y-ytofill]
        xtofill+=1
        ytofill+=1

#NE
#find y first
ytofill = 2
yminus1 = board[firstq_y-ytofill]  #this will give us list before current list
#find x next
xtofill = 1
xminus1 = yminus1[firstq_x-xtofill]  #this will give us letter before letter
#execute

if firstq_y>firstq_x:

    for NE in range(firstq_y):
        if yminus1[firstq_x-xtofill] == 0:
            yminus1[firstq_x-xtofill] = 'X'
        yminus1 = board[firstq_y-ytofill]
        xtofill-=1
        ytofill+=1

else:
    
    for NE in range(firstq_x):
        if yminus1[firstq_x-xtofill] == 0:
            yminus1[firstq_x-xtofill] = 'X'
        yminus1 = board[firstq_y-ytofill]
        xtofill-=1
        ytofill+=1

board = [a,b,c,d,e,f,g,h]
for row in board:
    for elem in row:
        print(elem, end=' ')
    print()

但是，它给了我一个错误：

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-4-cb78dab39eae> in <module>()
     54 
     55     for NE in range(firstq_y):
---> 56         if yminus1[firstq_x-xtofill] == 0:
     57             yminus1[firstq_x-xtofill] = 'X'
     58         yminus1 = board[firstq_y-ytofill]

IndexError: list index out of range

---------------------------------------------------------------------------
索引器回溯（最后一次最近调用）
在（）
54
55适用于范围内的NE（第一季度）：
--->56如果yminus1[firstq_x-xtofill]==0：
57 yminus1[firstq_x-xtofill]=“x”
58 yminus1=电路板[firstq_y-ytofill]
索引器：列表索引超出范围