Python：如何在嵌套列表中查找某些字符並返回索引

Question

我正在尋找一種方法來返回這些特定字符所在位置的索引元組列表。

例如，我想知道在我的嵌套列表中哪里有空格（“”）。

說我有這個：

board = [
        ["a", " ", " "],
        [" ", "x", " "],
        [" ", "b", " "]
    ]

我的 function 將是：

def empty_squares(board):
"""Return a list of the empty squares in the board, each as
   a (row, column) tuple"""

因此，如果我運行 function 它將返回[(0,1), (0,2), (1,0), (1,2), (2,0), (2,2)] 。

我只是不確定如何為嵌套列表執行此操作。

謝謝！

Answer 1

您可以遍歷電路板並使用 enumerate 來跟蹤索引。

l = []

for indexa, e in enumerate(board):
    for indexb, c in enumerate(e):
        if c == ' ':
            l.append((indexa, indexb))

或者簡單地使用列表理解：

l = [(indexa, indexb) for indexb, c in enumerate(e) for indexa, e in enumerate(board) if c == ' ']

兩者都會 output：

[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 2)]

Answer 2

也許與枚舉？

board = [
        ["a", " ", " "],
        [" ", "x", " "],
        [" ", "b", " "]
    ]

def empty_squares(board, symbol):
    """
    Return a list of the empty squares in the board, each as
    a (row, column) tuple
    """
    empty = []
    for row, sublist in enumerate(board):
        for column, item in enumerate(sublist):
            if item == symbol:
                empty.append((row, column))
    return empty

>>> empty_squares(board, ' ')
[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 2)]

Answer 3

最簡單的方法可能是使用numpy.where() 。

import numpy as np


board = [
    ["a", " ", " "],
    [" ", "x", " "],
    [" ", "b", " "]
]

idxs = [(i, j) for i, j in zip(*np.where(np.array(board) == ' '))]
print(idxs)