从mypy 0.990开始，mypy终于支持递归类型注解，使用自然语法：

from typing import Union, Dict, List

JSONVal = Union[None, bool, str, float, int, List['JSONVal'], Dict[str, 'JSONVal']]

d: JSONVal = {'a': ['b']}

mypy输出：

Success: no issues found in 1 source file

在0.990之前，这会产生一个错误，报告缺少递归类型支持：

$ mypy asdf.py
asdf.py:3: error: Recursive types not fully supported yet, nested types replaced with "Any"

在这样的版本中，Dict[str, Any]将是可行的方法。
现在还可以使用相互递归的类型别名，因此可以执行以下操作

from typing import Union, Dict, List

JSONVal = Union[None, bool, str, float, int, 'JSONArray', 'JSONObject']
JSONArray = List[JSONVal]
JSONObject = Dict[str, JSONVal]

d: JSONObject = {'a': ['b']}

Mypy现在支持递归类型。
截至2022年10月，该实现是临时的。您可以通过将enable_recursive_aliases = true标志添加到pyproject.toml来启用它。
从版本0.990开始，默认情况下将启用此功能。Source.

对于mypy的最新版本，对提到的MyPy问题跟踪器的这条注解建议使用协议来实现这一点，只要不需要使用TypeVar：

from __future__ import annotations

from collections.abc import Iterator
from typing import TypeVar, Protocol, overload, Any, TYPE_CHECKING

_T_co = TypeVar("_T_co")

class _RecursiveSequence(Protocol[_T_co]):
    def __len__(self) -> int: ...
    @overload
    def __getitem__(self, __index: int) -> _T_co | _RecursiveSequence[_T_co]: ...
    @overload
    def __getitem__(self, __index: slice) -> _RecursiveSequence[_T_co]: ...
    def __contains__(self, __x: object) -> bool: ...
    def __iter__(self) -> Iterator[_T_co | _RecursiveSequence[_T_co]]: ...
    def __reversed__(self) -> Iterator[_T_co | _RecursiveSequence[_T_co]]: ...
    def count(self, __value: Any) -> int: ...
    def index(self, __value: Any, __start: int = ..., __stop: int = ...) -> int: ...

def func1(a: _RecursiveSequence[int]) -> int: ...

if TYPE_CHECKING:
    reveal_type(func1([1]))         # Revealed type is "builtins.int"
    reveal_type(func1([[1]]))       # Revealed type is "builtins.int"
    reveal_type(func1([[[1]]]))     # Revealed type is "builtins.int"
    reveal_type(func1((1, 2, 3)))   # Revealed type is "builtins.int"
    reveal_type(func1([(1, 2, 3)])) # Revealed type is "builtins.int"
    reveal_type(func1([True]))      # Revealed type is "builtins.int"