如何为子类实例列表制作类型注释,例如连接两个列表? [英] How do I make a type annotation for a list of subclass instances, e.g to concatenate two lists?
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问题描述
我想遍历 List[A]
和 List[Subclass of A]
并执行相同的循环.我能看到的最好的方法是连接两个列表.然而,mypy 对此并不满意.
I want to iterate over List[A]
and List[Subclass of A]
and do the same loop. The best way I can see to do that is to concatenate the two lists. However, mypy is not happy about it.
如何将两者连接起来并让 mypy 开心?
How can I concatenate the two and keep mypy happy?
目前,我做# type: ignore[operator]
.如果可能,我想避免这种情况.
Currently, I do # type: ignore[operator]
. I would like to avoid that, if possible.
# Core Library modules
from typing import Iterable
# Third party modules
from pydantic import BaseModel
class Animal(BaseModel):
height: float
weight: float
class Cat(Animal):
lives: int = 7
cats = [Cat(height=1, weight=2, lives=7), Cat(height=3, weight=2, lives=1)]
animals = [Animal(height=9, weight=9)]
combined: Iterable[Animal] = cats + animals
for animal in combined:
print(animal)
给予
$ mypy untitled.py
untitled.py:20: error: Unsupported operand types for + ("List[Cat]" and "List[Animal]")
Found 1 error in 1 file (checked 1 source file)
推荐答案
出现这种情况是因为 list
是 invariant(提供了说明性示例).
This situation occurs because list
is invariant (provides an illustrative example).
我可以提供两种解决方案:
I can offer two solutions:
- 将两个列表显式定义为
List[Animal]
以成功连接:
- Explicitly define both lists as
List[Animal]
for successful concatenation:
cats: List[Animal] = [Cat(height=1, weight=2, lives=7), Cat(height=3, weight=2, lives=1)]
animals: List[Animal] = [Animal(height=9, weight=9)]
combined: Iterable[Animal] = cats + animals
for animal in combined:
print(animal)
- 使用 itertools.chain 进行连续迭代:
- Use itertools.chain for consecutive iteration:
cats = [Cat(height=1, weight=2, lives=7), Cat(height=3, weight=2, lives=1)]
animals = [Animal(height=9, weight=9)]
for animal in itertools.chain(cats, animals):
print(animal)
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