mypy 关于 numpy.apply_along_axis 的警告

编辑 2024 年 10 月 18 日：

下面显示了该问题的一个更为简单的重现。

mypy_arg_type.py：

import numpy as np
from numpy.typing import NDArray
import random

def winner(_: NDArray[np.bytes_]) -> bytes | None:
    return b"." if bool(random.randint(0, 1)) else None

board = np.full((2, 2), ".", "|S1")
for w in np.apply_along_axis(winner, 0, board):
    print(w)

>> python mypy_arg_type.py

b'.'
None

>> mypy mypy_arg_type.py

mypy_arg_type.py:9: error: Argument 1 to "apply_along_axis" has incompatible type "Callable[[ndarray[Any, dtype[bytes_]]], bytes | None]"; expected "Callable[[ndarray[Any, dtype[Any]]], _SupportsArray[dtype[Never]] | _NestedSequence[_SupportsArray[dtype[Never]]]]"  [arg-type]
mypy_arg_type.py:9: note: This is likely because "winner" has named arguments: "_". Consider marking them positional-only
Found 1 error in 1 file (checked 1 source file)

原始问题：

我正在研究一个问题，即根据棋盘上棋子的位置来确定四子连珠A游戏的获胜者。棋盘尺寸为 6x7，每列标有从到 的字母G。如果有获胜者，则在一行、一列、对角线或反对角线上有 4 个相同颜色的棋子。

例子：

输入：["A_Red", "B_Yellow", "A_Red", "B_Yellow", "A_Red", "B_Yellow", "G_Red", "B_Yellow"]

木板：

R Y . . . . R
R Y . . . . .
R Y . . . . .
. Y . . . . .
. . . . . . .
. . . . . . .

优胜者：Yellow

以下代码决定获胜者。

import itertools
import numpy as np
from numpy.typing import NDArray

def who_is_winner(pieces: list[str]) -> str:
    def parse_board() -> NDArray[np.bytes_]:
        m, n = 6, 7
        indices = [0] * n
        # https://numpy.org/doc/stable/user/basics.strings.html#fixed-width-data-types
        # One-byte encoding, the byteorder is ‘|’ (not applicable)
        board = np.full((m, n), ".", "|S1")
        for p in pieces:
            col = ord(p[0]) - ord("A")
            board[indices[col], col] = p[2]
            indices[col] += 1

        return board

    def winner(arr: NDArray[np.bytes_]) -> np.bytes_ | None:
        i = len(arr)
        xs = next(
            (xs for j in range(i - 3) if (xs := set(arr[j : j + 4])) < {b"R", b"Y"}),
            {None},
        )
        return xs.pop()

    def axis(x: int) -> np.bytes_ | None:
        # https://numpy.org/doc/2.0/reference/generated/numpy.apply_along_axis.html#numpy-apply-along-axis
        # Axis 0 is column-wise, 1 is row-wise.
        return next(
            (w for w in np.apply_along_axis(winner, x, board) if w is not None), None
        )

    def diag(d: int) -> np.bytes_ | None:
        # https://numpy.org/doc/stable/reference/generated/numpy.diagonal.html#numpy-diagonal
        # Diagonal number is w.r.t. the main diagonal.
        b = board if bool(d) else np.fliplr(board)
        return next(
            (w for d in range(-3, 4) if (w := winner(b.diagonal(d))) is not None), None
        )

    board = parse_board()
    match next(
        (
            w
            for f, i in itertools.product((axis, diag), (0, 1))
            if (w := f(i)) is not None
        ),
        None,
    ):
        case b"Y":
            return "Yellow"
        case b"R":
            return "Red"
        case _:
            return "Draw"

但是，这会产生如下的 mypy 违规：

error: Argument 1 to "apply_along_axis" has incompatible type "Callable[[ndarray[Any, dtype[bytes_]]], bytes_ | None]"; expected "Callable[[ndarray[Any, dtype[Any]]], _SupportsArray[dtype[bytes_]] | _NestedSequence[_SupportsArray[dtype[bytes_]]]]"  [arg-type]
note: This is likely because "winner" has named arguments: "arr". Consider marking them positional-only

根据apply_along_axis的文档，它应该返回一个值，这与上面的代码一致。

如何修复此违规？使函数winner仅定位于某一位置并没有什么区别，只是建议消失了。

我正在使用 Python 3.12.5 和 mypy 1.11.2。