用于解包对象的 Python 类型提示

Question

我正在尝试为对象解包实现类型提示。这是我目前拥有的

from typing import Tuple


class A:
    def __init__(self, x: int, y: str):
        self.x = x
        self.y = y

    def astuple(self) -> Tuple[int, str]:
        return self.x, self.y

    # Need to annotate the return type of __iter__
    def __iter__(self):
        return iter(self.astuple())


a = A(1, "a")
# This cannot infer the type of x and y
x, y = a
reveal_type(x)
reveal_type(y)
# This infers the type of p and q as int and str respectively
p, q = a.astuple()
reveal_type(p)
reveal_type(q)

打印

$ mypy unpack_object.py
unpack_object.py:20: note: Revealed type is "Any"
unpack_object.py:21: note: Revealed type is "Any"
unpack_object.py:24: note: Revealed type is "builtins.int"
unpack_object.py:25: note: Revealed type is "builtins.str"
Success: no issues found in 1 source file

但是，我希望 mypy 能够推断出 x、y (int、str) 的正确类型。我怎样才能实现这个目标？

Answer 1

无法在 Python 中定义自己的异构可迭代类型。使 A 成为 NamedTuple 的子类。

from typing import NamedTuple


class A(NamedTuple):
    x: int
    y: str


x, y = A(1, "a")
reveal_type(x)  # builtins.int
reveal_type(y)  # builtins.str