数独求解器 - 切片索引必须是整数或无或具有__index__方法

Question

我正在尝试为我的Sudoku Solver编写一个求解器，但是当我运行我的数独求解器时，我收到以下错误。我不明白问题是什么。我看其他问题，但也无法解决问题。 以下是我的代码和问题：

import numpy as np

class SolveSudoku(object):
    def __init__(self,grid):
        self.grid = grid

    def _check_row(self,digit,row):
        return digit not in self.grid[row,:]

    def _check_column(self,digit,column):
        return digit not in self.grid[:,column]

    def _check_box(self,digit,row,col):
        rc = (row/3)*3
        cc = (col/3)*3
        return digit not in self.grid[rc:rc+3,cc:cc+3]

    def _check_safe(self,digit,row,col):
        return self._check_box(digit,row,col) \
               and self._check_row(digit,row) \
               and self._check_column(digit,col)

    def _find_empty(self,stop):
        if 0 in self.grid:
            stop[0] = np.where(self.grid==0)[0][0]
            stop[1] = np.where(self.grid==0)[1][0]
            return True
        else:
            return False

    def _solve(self):
        stop = [0,0]
        if not self._find_empty(stop):
            return True
        for digit in np.arange(1,10):
            row = stop[0]
            col = stop[1]
            if self._check_safe(digit,row,col):
                self.grid[row,col] = digit
                if self._solve():
                    return True
                self.grid[row,col]=0
        return False

    def solve(self):
        if self._solve():
            return self.grid
        raise("Sudoku can not be solved")

File "solve.py", line 117, in <module>
        grid = sudoku.solve()
      File "C:\Users\Erke\.spyder-py3\SudokuSolver-master\sudoku.py", line 47, in solve
        if self._solve():
      File "C:\Users\Erke\.spyder-py3\SudokuSolver-master\sudoku.py", line 39, in _solve
        if self._check_safe(digit,row,col):
      File "C:\Users\Erke\.spyder-py3\SudokuSolver-master\sudoku.py", line 20, in _check_safe
        return self._check_box(digit,row,col) \
      File "C:\Users\Erke\.spyder-py3\SudokuSolver-master\sudoku.py", line 17, in _check_box
        return digit not in self.grid[rc:rc+3,cc:cc+3]
    TypeError: slice indices must be integers or None or have an __index__ method