[英]Python check attribute type in inherited abstract class
I have a basic abstract class structure such as the following:我有一个基本的抽象 class 结构,如下所示:
from abc import ABCMeta, abstractmethod
class BaseClass(metaclass=ABCMeta):
@property
@abstractmethod
def class_name(self):
pass
@property
@abstractmethod
def class_val(self):
pass
@abstractmethod
def foo(self):
pass
def bar(self):
# do something
class ChildClass1(BaseClass):
class_name = "Child1"
class_val = 1
def foo(self):
# do something else
class ChildClass2(BaseClass):
class_name = "Child2"
class_val = 2
def foo(self):
# do something else again
This works to basically do what I want, ie, it lets me define variations of a base class which share the same implementation of the method bar()
but have different implementations of foo()
, with different class-specific attributes -- all of which must be implemented in the child classes, otherwise it raises the error TypeError: Can't instantiate abstract class ChildClass1 with abstract methods class_name
(for example, if I try implement it without the class_name
class attribute).这基本上可以做我想做的事,即,它让我定义一个基类 class 的变体,它们共享方法bar()
的相同实现,但具有不同的foo()
实现,具有不同的类特定属性——所有必须在子类中实现,否则会引发错误TypeError: Can't instantiate abstract class ChildClass1 with abstract methods class_name
(例如,如果我尝试在没有class_name
class 属性的情况下实现它)。
This is almost what I want.这几乎就是我想要的。 However I would like to know if there is any way I can force the child classes to have a string type for the class_name
attribute, an int
type for the class_val
attribute, etc.?但是我想知道是否有任何方法可以强制子类的class_name
属性具有字符串类型, class_val
属性具有int
类型等?
The best thing to do would be to use type hints , and then validate the type hints using a third party tool such as mypy
:最好的办法是使用类型提示,然后使用第三方工具(如mypy
)验证类型提示:
class BaseClass(metaclass=ABCMeta):
@property
@abstractmethod
def class_name(self) -> str:
pass
@property
@abstractmethod
def class_val(self) -> int:
pass
@abstractmethod
def foo(self):
pass
def bar(self):
pass
If you try to define a subclass with the wrong types for the properties, mypy
will throw an error, eg with:如果您尝试为属性定义错误类型的子类, mypy
将抛出错误,例如:
class ChildClass2(BaseClass):
class_name = "Child2"
class_val = "a"
def foo(self):
pass
you'd get the error along the lines of:你会得到如下错误:
test.py: error: Incompatible types in assignment
(expression has type "str", base class "BaseClass" defined the type as "int")
This technically doesn't stop someone from defining a subclass that has the wrong type, since the Python runtime ignores type hints.这在技术上不会阻止某人定义具有错误类型的子类,因为 Python 运行时会忽略类型提示。 However, an approach that raises an error if a bad type is encountered would likely need a call to isinstance()
for each instance variable, which would become unwieldy if you have a lot of properties that you want to enforce the types for.但是,如果遇到错误类型则引发错误的方法可能需要为每个实例变量调用isinstance()
,如果您有许多要为其强制执行类型的属性,这将变得笨拙。
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