英文:
TypeVar in python
问题
I ran the following code in Jupyter Notebook:
%load_ext nb_mypy
from typing import Any, List, Union, TypeVar
T = TypeVar("T", int, str)
def first(container: List[T]) -> T:
return container[2]
ls: List[Any] = [1, "hello", ("hello",)]
first(ls)
And the result was:
('hello',)
Here, I constrained the variable T to represent only str or int types. Then, I constrained the container parameter of the function. I believed that the elements in the container could only be of type int or str, but when I tried to pass a list ls containing tuples, mypy did not report an error. I cannot understand why.
Doesn't List[T] mean that the container can only contain variables of type T? Here, I also constrained the return value of the function to be of type T, but it seems to have had no effect, as the function still returned a tuple, and mypy did not report any errors.
英文:
I ran the following code in Jupyter Notebook:
%load_ext nb_mypy
from typing import Any, List, Union, TypeVar
T = TypeVar("T",int,str)
def first(container: List[T]) -> T:
return container[2]
ls: List[Any] = [1,"hello",("hello",)]
first(ls)
And the result was:
('hello',)
Here, I constrained the variable T to represent only str or int types. Then, I constrained the container parameter of the function. I believed that the elements in container could only be int or str, but when I tried to pass a list ls containing tuples, mypy did not report an error. I cannot understand why.
Doesn't List[T] mean that container can only contain variables of type T? Here, I also constrained the return value of the function to be of type T, but it seems to have had no effect, as the function still returned a tuple, and mypy did not report any errors.
答案1
得分: 1
你已将 ls 注释为 List[Any]。Any 是 Mypy 的逃逸口，告诉它不要进行类型检查，并接受对象上的任何操作。例如，
x: Any = 3
x + "foo"
可以很好地进行类型检查。如果删除 List[Any] 提示，或将其更改为 list[object] 或 list[int | str | tuple[str]]（Python 3.10+ 语法），则会收到错误消息，正如您所期望的那样。
此问题的答案可能会有所帮助。
英文:
You've annotated ls as List[Any]. Any is Mypy's escape hatch, that tells it not to type check, and to accept any operation on the object. For instance,
x: Any = 3
x + "foo"
type checks just fine. If you remove the List[Any] hint, or change it list[object] or list[int | str | tuple[str]] (Python 3.10+ syntax), you get an error as you'd expect.
The answer to this question may be of help.
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论