为啥在遍历列表矩阵时出现列表索引超出范围错误？

Posted 2023-02-21

【中文标题】为啥在遍历列表矩阵时出现列表索引超出范围错误？

【英文标题】：Why am I getting a list index out of range error when traversing a list matrix?为什么在遍历列表矩阵时出现列表索引超出范围错误？

【发布时间】：2020-12-03 12:49:16

【问题描述】：

我正在尝试遍历矩阵列表，即（向右移动 3 个值，向下移动 1 个值）并看到上述错误。预期值正在打印到控制台，这表明该值存在并且没有超出范围。

grid = []

with open(filename) as f:
    for line in f.readlines():
        line.strip()
        grid.append(line)
print(grid)

col = 2
row = 0
count = 0

for i in enumerate(grid):
    row = row + 1
    print(grid[row][col])
    if grid[row][col] == "#":
        print("found")
        print(grid[row][col])
        count = count+1
    col = col + 3

如果我不增加 row 和 col 值，这个问题也会持续存在。我的输入数据在这里：

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【问题讨论】：

如果在不增加行和列值的情况下问题仍然存在，则很可能意味着网格中的列数少于三。您是否正确读取数据？ （如果您发布一个最小的可重现示例，这肯定会有所帮助，因为我们看不到您的数据，这使得调试有点困难）

此外，您同时遍历行和列，这有点令人困惑。你可能不想这样做。 （除非你真的这样做，在这种情况下，我很抱歉成为聪明人。）

是的。现在我确定了。您的代码将在循环的第 11 次迭代时失败，因为它将尝试访问第 32 列。不幸的是，您只有 31 个，因此出现错误。

【参考方案1】：

Python 列表（和矩阵）的索引为零。

您过早地将 1 添加到该行，因此在最后一行中您尝试访问最后一行之后不存在的行。尝试将row = row + 1 放在col = col + 1 之前。然后从那里继续调试。

或者，您可以从 row = -1 开始，它应该可以工作，但它有点“脏”。

此外，由于您已经在使用枚举，您可能需要考虑

for idx, i in enumerate(grid):
    grid[idx][col] == '#'

因为 enumerate 已经为您提供了所需的索引。

【讨论】：

您的解决方案适用于小型数据集，但是在尝试使用较大的数据集时我看到了同样的错误。我已经尝试将值设置为 -1 并重新定位增量语句。另外，我需要手动增加行和列，而不是以线性方式遍历 - 我可以按照您发布的建议执行此操作吗？

在这种情况下，我刚刚在您的 cmets 中发布了另一部分 - 您同时遍历行和列，这仅适用于您的列数至少是 3 倍的情况作为当前行索引。这是我不会打赌的。您可能想要在里面进行第二个循环，它会遍历列。或者这背后的某种其他逻辑。不要盲目地将每行的 col 索引增加三个。