如何键入(在 Python 中,例如对于 MyPy)一个需要两个参数的函数——一个枚举和它的值/成员之一?
from enum import Enum
from typing import TypeVar, Type
class MyEnumA(Enum):
A = 1
B = 2
class MyEnumB(Enum):
A = 1
B = 2
TE = TypeVar('TE', bound=Enum)
def myfunction(member: TE, e: Type[TE]) -> None:
pass
myfunction(MyEnumA.A, MyEnumA) # all right
myfunction(MyEnumA.A, MyEnumB) # I expect mypy-error here but it passed
print(type(MyEnumA.A)) # says: <enum 'MyEnumA'>
print(type(MyEnumB.A)) # says: <enum 'MyEnumB'>
print(f'{isinstance(MyEnumA.A, MyEnumA)=}') # says: isinstance(MyEnumA.A, MyEnumA)=True
print(f'{isinstance(MyEnumA.A, MyEnumB)=}') # says: isinstance(MyEnumA.A, MyEnumB)=False
reveal_type(MyEnumA) # mypy: Revealed type is "def (value: builtins.object) -> e.MyEnumA"
reveal_type(MyEnumA.A) # mypy: Revealed type is "Literal[e.MyEnumA.A]?"
我想了解
myfunction
以便 MyPy 在那里检测到错误。关键观察是 MyPy 实际上认为类 MyEnumA 是什么:
reveal_type(MyEnumA) # mypy: Revealed type is "def (value: builtins.object) -> e.MyEnumA"
它给出了注释
myfunction
的线索,无论它多么不明显:
P = ParamSpec('P')
def myfunction(member: TE, e: Callable[P, TE]) -> None:
这使得 MyPy 在
myfunction
的第二次调用中发现输入错误:
error: Argument 2 to "myfunction" has incompatible type "Type[MyEnumA]"; expected "Callable[[object], MyEnumB]" [arg-type]
根据 mypy 文档,任何类都是有效类型,因此对于绑定类型变量,它应该只是
MyEnumA
这将绑定它只接受您的特定类型的 Enum 子类,而不是所有扩展基类的 Enum 类.然后引用你想要一个参数只接受不同类型的枚举,你会使用Type[...]
,所以结果是这个代码:
from enum import Enum
from typing import TypeVar, Type
class MyEnumA(Enum):
A = 1
B = 2
class MyEnumB(Enum):
A = 1
B = 2
TE = TypeVar('TE', bound=MyEnumA)
def myfunction(member: TE, e: Type[TE]) -> None:
pass
myfunction(MyEnumA.A, MyEnumA) # all right
myfunction(MyEnumB.A, MyEnumB) # I expect mypy-error here but it passed
您需要在哪里更改传递给
TypeVar
的枚举,但它会产生您想要的结果:
test.py:17: error: Value of type variable "TE" of "myfunction" cannot be "MyEnumB" [type-var] Found 1 error in 1 file (checked 1 source file)