即使使用复制方法，Python列表也会无缘无故地改变。

Question

def return_solved_board(board):
    solution = board.copy()

回溯递归循环开始

def solve(board): 
    for y in range(9):
        for x in range(9):
            if solution[y][x] == 0:
                for number in range(1,10):
                    if check_rules_at_point(x, y, number, solution):
                        solution[y][x] = number
                        solve(solution)
    #Where backtracking comes into play, if the solve method fails on the next cell than it resets current one.
                        solution[y][x] = 0
    #Breaks out of recursion to try a differant number in cell prior
                return
    #Stores a solved copy of the solution into global variable
    global returned_information
    returned_information = solution.copy()
    print(returned_information) #1st print statement

检查棋盘是否能解开。

if not check_for_valid_board(board):
    return "This board is not possible to solve."
else:
    solve(board)
    global returned_information
    print(returned_information) #2nd print statement
    return returned_information

print(return_solved_board(valid_sudoku_board1))

我想写一个解数独谜题的程序。谜题被存储在一个列表中。当我运行这个程序时，第一条print语句返回正确的解题列表。然而，第二条返回语句返回的是原来的未解谜题。它们的id都是一样的，但是我不明白为什么第二条打印语句中的return_information会变回来，因为return_information只被调用了一次。

Answer 1

你可能会碰到dicts'list'。copy() 浅尝辄止 copy.deepcopy(...) 而不是去做深度复制。