问题描述
以下代码产生了一个 - 可以理解但错误的 - 来自 mypy 的错误:
from typing import List,Union,Any
class classA():
def __init__(self,name: str) -> None:
self.__name = name
def __eq__(self,other: Any) -> bool:
if (type(self) == type(other)):
return (self.name == other.name)
return False
@property
def name(self) -> str:
return self.__name
class classB():
def __init__(self,id: int) -> None:
self.__id = id
def __eq__(self,other: Any) -> bool:
if (type(self) == type(other)):
return (self.id == other.id)
return False
@property
def id(self) -> int:
return self.__id
class classC():
def __init__(self) -> None:
self.__elements: List[Union[classA,classB]] = list()
def add(self,elem: Union[classA,classB]) -> None:
if (elem not in self.__elements):
self.__elements.append(elem)
def get_a(self,name_of_a: str) -> classA:
tmp_a = classA(name_of_a)
if (tmp_a in self.__elements):
return self.__elements[self.__elements.index(tmp_a)]
raise Exception(f'{name_of_a} not found')
def get_b(self,id_of_b: int) -> classB:
tmp_b = classB(id_of_b)
if (tmp_b in self.__elements):
return self.__elements[self.__elements.index(tmp_b)]
raise Exception(f'{id_of_b} not found')
调用“mypy --show-error-codes classes.py”显示以下输出:
classes.py:43:错误:不兼容的返回值类型(得到“Union[classA,classB]”,预期为“classA”)[返回值]
classes.py:49:错误:不兼容的返回值类型(得到“Union[classA,classB]”,预期为“classB”)[返回值]
在 1 个文件中发现 2 个错误(检查了 1 个源文件)
如何告诉 mypy 函数 get_a 只会返回 classA?
解决方法
您可以使用 assert 告诉 mypy:
def get_a(self,name_of_a: str) -> classA:
tmp_a = classA(name_of_a)
if (tmp_a in self.__elements):
result = self.__elements[self.__elements.index(tmp_a)]
assert isinstance(result,classA)
return result
raise Exception(f'{name_of_a} not found')