python - 如何为子类实例列表制作类型注释,例如连接两个列表?
问题描述
我想迭代List[A]
并List[Subclass of A]
做同样的循环。我能看到的最好的方法是连接两个列表。但是,mypy 对此并不满意。
我怎样才能将两者连接起来并让 mypy 开心?
目前,我这样做# type: ignore[operator]
。如果可能的话,我想避免这种情况。
MVCE
# 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
$ 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)
解决方案
出现这种情况是因为list
它是不变的(提供说明性示例)。
我可以提供两种解决方案:
- 明确定义两个列表以
List[Animal]
实现成功连接:
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:
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)