mypy 不兼容类型列表<nothing>具有类型列表<str>

Question

我正在使用提示工具包python库，代码为：

from __future__ import annotations
from prompt_toolkit.shortcuts import checkboxlist_dialog
results: list[str] = checkboxlist_dialog(
title="CheckboxList dialog",
text="What would you like in your breakfast ?",
values=[
("eggs", "Eggs"),
("bacon", "Bacon"),
("croissants", "20 Croissants"),
("daily", "The breakfast of the day"),
],
).run()

当我运行mypy 0.931时，我得到：

test.py:4: error: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "List[str]")
test.py:4: note: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
test.py:4: note: Consider using "Sequence" instead, which is covariant
test.py:7: error: Argument "values" to "checkboxlist_dialog" has incompatible type "List[Tuple[str, str]]"; expected "Optional[List[Tuple[<nothing>, Union[str, MagicFormattedText, List[Union[Tuple[str, str], Tuple[str, str, Callable[[MouseEvent], None]]]], Callable[[], Any], None]]]]"

我不确定问题是否出在我的代码上，因为返回值类似于['eggs', 'bacon']，它是list[str]。mypy的这个错误也很奇怪，因为我认为我不应该在这里使用协变。有什么问题的线索吗？

Answer 1

我认为问题是mypy对checkboxlist_dialog函数的信息很少，当然也不知道它的返回类型可以从value参数中计算出来。

你可能不得不写：

from typing import cast
results = cast(list[string], checkboxlist_dialog(....))

它告诉mypy你知道你在做什么，而返回类型实际上是list[string]，不管它怎么想。