Unsoundness with `typing.IO` and friends
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還沒有人認領這個 Issue。
評估
研究方向
首先檢視 typing.IO、typing.BinaryIO、typing.TextIO 和 io.BytesIO 的執行期行為，以及它們與 typeshed 的關係和所連結的 CPython issue。比較提出的三種方法，並記錄或實作一份已達成共識的規格和執行期方向；完成的要求是解決 isinstance() 和 issubclass() 應如何運作。
由索引模型根據 Issue 內容生成。
描述
The classes typing.IO, typing.BinaryIO, and typing.TextIO look like they want to be Protocols or ABCs, but in fact they are defined as regular generic classes, both at runtime and in typeshed. However, they are meant to encompass the concrete IO classes defined in the io module, and in typeshed we implement that by having these classes inherit from typing.*IO classes, even though there is no such inheritance at runtime.
This can easily lead to unsound behavior:
import io, typing
def f(x: int | io.BytesIO) -> int:
if isinstance(x, typing.BinaryIO):
return x.fileno()
return x
f(io.BytesIO()) + 1 # boom
Type checkers think BytesIO is a subclass of BinaryIO, because that's how it's defined in typeshed, but in fact it isn't at runtime.
I can see a few solutions:
- Special-case
typing.*IOin the spec and say that type checkers should rejectisinstance()/issubclass()calls involving them. - Deprecate the
typing.*IOclasses and eventually remove them, nudging people to use their own Protocols (or the newio.Reader/io.Writer) instead. This is conceptually clean but may be annoying for a lot of users; the typing classes are nice to use in simple application code. - Make these classes actually (runtime-checkable?) Protocols at runtime, though they would be unwieldily large.
Even if we do (2) or (3) type checkers might still want to do (1) since it will be a while before the relevant runtime changes take effect.
(Noticed this while looking into https://github.com/python/cpython/issues/133492 .)
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從這裡開始
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python/typing 的其他 Issue
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