如何让Mypy意识到对两个整数进行排序会返回两个整数 [英] How to get Mypy to realize that sorting two ints gives back two ints

问题描述

我的代码如下:

from typing import Tuple

a: Tuple[int, int] = tuple(sorted([1, 3]))

Mypy告诉我:

分配中的类型不兼容(表达式的类型为"Tuple [int， ...]，变量的类型为" Tuple [int，int])

Incompatible types in assignment (expression has type "Tuple[int, ...]", variable has type "Tuple[int, int]")

我做错了什么? Mypy为什么无法弄清楚排序后的元组将恰好返回两个整数?

What am I doing wrong? Why can't Mypy figure out that the sorted tuple will give back exactly two integers?

推荐答案

对sorted的调用将生成一个List[int]，该cc>不包含有关长度的信息.这样，从中生成元组也没有有关长度的信息.元素的数量完全不受您使用的类型的定义.

The call to sorted produces a List[int] which carries no information about length. As such, producing a tuple from it also has no information about the length. The number of elements simply is undefined by the types you use.

在这种情况下，您必须告诉您的类型检查器信任您.使用# type: ignore或cast无条件地将目标类型视为有效:

You must tell your type checker to trust you in such cases. Use # type: ignore or cast to unconditionally accept the target type as valid:

# ignore mismatch by annotation
a: Tuple[int, int] = tuple(sorted([1, 3]))  # type: ignore
# ignore mismatch by cast
a = cast(Tuple[int, int], tuple(sorted([1, 3])))

或者，创建一个可识别长度的排序:

Alternatively, create a lenght-aware sort:

 def sort_pair(a: T, b: T) -> Tuple[T, T]:
     return (a, b) if a < b else (b, a)

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