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[英]Python using child class's class attribute as default parameter without overriding method
[英]Python overriding type hint on a method's return in child class, without redefining method signature
我有一個基礎 class 在方法返回時帶有float
類型提示。
在子 class 中,在不重新定義簽名的情況下,我可以以某種方式將方法返回的類型提示更新為int
嗎?
示例代碼
#!/usr/bin/env python3.6
class SomeClass:
"""This class's some_method will return float."""
RET_TYPE = float
def some_method(self, some_input: str) -> float:
return self.RET_TYPE(some_input)
class SomeChildClass(SomeClass):
"""This class's some_method will return int."""
RET_TYPE = int
if __name__ == "__main__":
ret: int = SomeChildClass().some_method("42"). #
ret2: float = SomeChildClass().some_method("42")
我的 IDE 抱怨類型不匹配:
發生這種情況是因為我的 IDE 仍在使用SomeClass.some_method
的類型提示。
研究
我認為解決方案可能是使用 generics,但我不確定是否有更簡單的方法。
建議可能使用實例變量注釋,但我不確定如何為返回類型執行此操作。
以下代碼在 PyCharm 上運行良好。 我添加了complex
的案例以使其更清晰。
我基本上將該方法提取到通用 class 中,然后將其用作每個子類的 mixin。 請格外小心使用,因為它似乎相當不標准。
from typing import ClassVar, Generic, TypeVar, Callable
S = TypeVar('S', bound=complex)
class SomeMethodImplementor(Generic[S]):
RET_TYPE: ClassVar[Callable]
def some_method(self, some_input: str) -> S:
return self.__class__.RET_TYPE(some_input)
class SomeClass(SomeMethodImplementor[complex]):
RET_TYPE = complex
class SomeChildClass(SomeClass, SomeMethodImplementor[float]):
RET_TYPE = float
class OtherChildClass(SomeChildClass, SomeMethodImplementor[int]):
RET_TYPE = int
if __name__ == "__main__":
ret: complex = SomeClass().some_method("42")
ret2: float = SomeChildClass().some_method("42")
ret3: int = OtherChildClass().some_method("42")
print(ret, type(ret), ret2, type(ret2), ret3, type(ret3))
例如,如果您將ret2: float
更改為ret2: int
,它將正確顯示類型錯誤。
可悲的是, mypy在這種情況下確實顯示錯誤(版本 0.770),
otherhint.py:20: error: Incompatible types in assignment (expression has type "Type[float]", base class "SomeClass" defined the type as "Type[complex]")
otherhint.py:24: error: Incompatible types in assignment (expression has type "Type[int]", base class "SomeClass" defined the type as "Type[complex]")
otherhint.py:29: error: Incompatible types in assignment (expression has type "complex", variable has type "float")
otherhint.py:30: error: Incompatible types in assignment (expression has type "complex", variable has type "int")
第一個錯誤可以通過編寫來“修復”
RET_TYPE: ClassVar[Callable] = int
對於每個子類。 現在,錯誤減少到
otherhint.py:29: error: Incompatible types in assignment (expression has type "complex", variable has type "float")
otherhint.py:30: error: Incompatible types in assignment (expression has type "complex", variable has type "int")
這與我們想要的恰恰相反,但如果你只關心 PyCharm,那也沒關系。
你可以使用類似的東西:
from typing import TypeVar, Generic
T = TypeVar('T', float, int) # types you support
class SomeClass(Generic[T]):
"""This class's some_method will return float."""
RET_TYPE = float
def some_method(self, some_input: str) -> T:
return self.RET_TYPE(some_input)
class SomeChildClass(SomeClass[int]):
"""This class's some_method will return int."""
RET_TYPE = int
if __name__ == "__main__":
ret: int = SomeChildClass().some_method("42")
ret2: float = SomeChildClass().some_method("42")
但是有一個問題。 那我不知道怎么解決。 對於 SomeChildClass 方法 some_method IDE 將顯示通用提示。 至少 pycharm(我想你是這個)不會將其顯示為錯誤。
好的,所以我可以嘗試並結合@AntonPomieshcheko 和@KevinLanguasco 的答案來提出一個解決方案,其中:
mypy
報告這正是我想要的行為。 非常感謝大家:)
#!/usr/bin/env python3
from typing import TypeVar, Generic, ClassVar, Callable
T = TypeVar("T", float, int) # types supported
class SomeBaseClass(Generic[T]):
"""This base class's some_method will return a supported type."""
RET_TYPE: ClassVar[Callable]
def some_method(self, some_input: str) -> T:
return self.RET_TYPE(some_input)
class SomeChildClass1(SomeBaseClass[float]):
"""This child class's some_method will return a float."""
RET_TYPE = float
class SomeChildClass2(SomeBaseClass[int]):
"""This child class's some_method will return an int."""
RET_TYPE = int
class SomeChildClass3(SomeBaseClass[complex]):
"""This child class's some_method will return a complex."""
RET_TYPE = complex
if __name__ == "__main__":
some_class_1_ret: float = SomeChildClass1().some_method("42")
some_class_2_ret: int = SomeChildClass2().some_method("42")
# PyCharm can infer this return is a complex. However, running mypy on
# this will report (this is desirable to me):
# error: Value of type variable "T" of "SomeBaseClass" cannot be "complex"
some_class_3_ret = SomeChildClass3().some_method("42")
print(
f"some_class_1_ret = {some_class_1_ret} of type {type(some_class_1_ret)}\n"
f"some_class_2_ret = {some_class_2_ret} of type {type(some_class_2_ret)}\n"
f"some_class_3_ret = {some_class_3_ret} of type {type(some_class_3_ret)}\n"
)
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