Allow creating type aliases with type checked metadata attached

Annotations in Python have many use cases beyond static type checking. I'd really like to be able to create a type that is an alias to another type while also attaching metadata to it. The idea is to be able to use MyPy's type system but also use annotations for other use cases such as runtime validation at the same time. I'm thinking something along these lines (though I have no idea how this would work in practice):

from datetime import datetime
from mypy_extensions import TypedDict
from somewhere import AliasWithMetadata

# define metadata type
Options = TypedDict('Options', {'min': int, 'max': int})
# define type alias with allowed metadata
MinMaxInt = AliasWithMetadata(int, Options)

# define age arg as type int with metadata attached
def get_rough_birth_year(age: MinMaxInt(min=0, max=120)):
    return datetime.today().year - age

# call function with int without mypy complaining
get_rough_birth_year(105)

未确定文件、测试或实现入口点。首先审查提议的 AliasWithMetadata 示例以及现有的 Python typing 和 MyPy 行为，然后明确所需的静态检查和运行时元数据语义。要视为完成，需要就定义和使用此类别名达成一致的设计，并记录其行为。