mypy：如何将 "convert" 可变长度元组变回固定长度元组？

Question

Python代码：

t = (1,2,3)
t = tuple(x+1 for x in t)

mypy抱怨：

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

我应该怎么做才能避免该错误？这没有帮助：

t = (1,2,3)
t = tuple(x+1 for x in t)[0:3]

这个"works":

from typing import Tuple
t: Tuple[int, ...] = (1,2,3)
t = tuple(x+1 for x in t)

但我实际上不希望t成为一个可变长度的元组。

我当然可以告诉 mypy 忽略这一行：

t = (1,2,3)
t = tuple(x+1 for x in t) # type: ignore

或者重复一遍：

t = (1,2,3)
t = (t[0]+1, t[1]+1, t[2]+1)

或者使用临时变量至少避免重复 +1 部分（这在现实世界的问题中更复杂）：

t = (1,2,3)
tmp = tuple(x+1 for x in t)
t = (tmp[0], tmp[1], tmp[2])

有没有更好的解决方案？

Answer 1

您可以使用 cast 来解决这个问题。

from typing import cast, Tuple

t = (1,2,3)

t = cast(Tuple[int, int, int], tuple(x+1 for x in t))

mypy: How to "convert" variable length tuple back to fixed length tuple?