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python - 为什么返回 TypeError：“NoneType”类型的对象没有 len()

问题描述

Python 3.8.2 Mac 大苏尔 11.2.1

这段代码应该是终端中的一个简单的扫雷游戏，但是当我运行它时，我只收到一条错误消息（如下所示）我在四处搜索时找不到解决这个问题的任何帮助，所以我想自己问一下

import random
import re

class Board:
    def __init__(self, dim_size, num_bombs):
        self.dim_size = dim_size
        self.num_bombs = num_bombs

        self.board = self.make_new_board() 
        self.assign_values_to_board

        self.dug = set() 

    def make_new_board(self):
        board = [[None for _ in range(self.dim_size)] for _ in range(self.dim_size)]

    def assign_values_to_board(self):
        for r in range(self.dim_size):
            for c in range(self.dim_size):
                if self.board[r][c] == '*':
                    continue
                self.board[r][c] = self.get_num_neighboring_bombs(r, c)

    def get_num_neighboring_bombs(self, row, col):
        num_neighboring_bombs = 0
        for r in range(max(0, row-1), min(self.dim_size-1, row+1)+1):
            for c in range(max(0, col-1), min(self.dim_size - 1, col+1)+1):
                if r == row and c == col:
                     continue
                if self.board[r][c] == '*':
                    num_neighboring_bombs += 1

        return num_neighboring_bombs

        bombs_planted = 0
        while bombs_planted < self.num_bombs:
            loc = random.randint(0, self.dim_size**2 - 1)
            row = loc // self.dim_size
            col = loc % self.dim_size

            if board [row][col] == '*':
                # bomb already plated here
                continue

            board[row][col] = '*' # plant the bomb
            bombs_planted += 1

        return board

    def dig(self, row, col):
        self.dug.add((row, col))

        if self.board[row][col] == '*':
            return False
        elif self.board[row][col] > 0:
            return True

        for r in range(max(0, row-1), min(self.dim_size-1, row+1)+1):
            for c in range(max(0, col-1), min(self.dim_size - 1, col+1)+1):
                if (r, c) in self.dug:
                    continue
                self.dig(r, c)

        return True

    def __str__(self):
        visible_board = [[None for _ in range(self.dim_size)] for _ in range(self.dim_size)]
        for row in range(self.dim_size):
            for col in range(self.dim_size):
                if (row,col) in self.dug:
                    visible_board[row][col] = str(self.board[row][col])
                else: 
                    visible_board[row][col] = ' '

            string_rep = ''

            widths = []
            for idx in range(self.dim_size):
                columns = map(lambda x: x[idx], visible_board)
                widths.append(
                    len(
                        max(columns, key = len)
                    )
                )

            indices = [i for i in range(self.dim_size)]
            indices_row = '   '
            cells = []
            for idx, col in enumerate(indices):
                format = '%-' + str(widths[idx]) + "s"
                cells.append(format % (col))
            indices_row += '  '.join(cells)
            indices_row += '  \n'

            for i in range(len(visible_board)):
                row = visible_board[i]
                string_rep += f'{i} |'
                cells = []
                for idx, col in enumerate(row):
                    format = '%-' + str(widths[idx]) + "s"
                    cells.append(format % (col))
                string_rep += ' |'.join(cells)
                string_rep += ' |\n'

            str_len = int(len(string_rep) / self.dim_size)
            string_rep = indices_row + '-'*str_len + '\n' + string_rep + '-'*str_len

            return string_rep

def play(dim_size=10, num_bombs=10):
    board = Board(dim_size, num_bombs)
    safe = True

    while len(board.dug) < board.dim_size ** 2 - num_bombs:
        print(board)
        user_input = re.split(',(\\s)*', input("Where would you like to dig? Input as row,col: "))
        row, col = int(user_input[0]), int(user_input[-1])
        if row < o or row >= board.dim_size or col < 0 or col >= dim_size:
            print("Invalid location. Try again")
            continue

        safe = board.dig(row, col)
        if not safe:
            break

    if safe:
        print("Victory Royale!")
    else:
        print("You suck. Game Over")
        board.dug = [(r,c) for r in range(board.dim_size) for c in range(board.dim_size)]
        print(board)

if __name__ == '__main__':
    play()

当我运行此代码时，它只返回

Traceback (most recent call last):
  File "/Users/henry/Documents/projects/GamesPython/Minesweeper/game.py", line 134, in <module>
    play()
  File "/Users/henry/Documents/projects/GamesPython/Minesweeper/game.py", line 115, in play
    print(board)
  File "/Users/henry/Documents/projects/GamesPython/Minesweeper/game.py", line 82, in __str__
    max(columns, key = len)
TypeError: object of type 'NoneType' has no len()

我该如何解决这个问题

标签： python

解决方案

可迭代对象columns中至少有一个None值。这是一个简单的示例，它在给定相同的代码行的情况下提供相同的错误：

columns = [ "a", None, "b" ]
max(columns, key = len)

结果：

max(columns, key = len)
TypeError: object of type 'NoneType' has no len()

至于为什么该None值在那里，columns是从visible_board. 我没有花时间完全理解你的逻辑，但我会指出构建的代码行visible_board非常可疑：

visible_board = [[None for _ in range(self.dim_size)] for _ in range(self.dim_size)]

当然在我看来它会建立一个包含很多None条目的列表。在调试器中运行代码时会验证这一点。在发生错误时，visible_board如下所示：

[[''，''，''，''，''，''，''，''，''，'']，[无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无，无]，[无，无，无，无，无，无，无，无，无，无，无]]

len因此，您最终尝试在一个值上调用属性None并得到您所做的错误也就不足为奇了。

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