如何在Python中使类或方法抽象?
我尝试像这样重新定义__new__():
class F:
def __new__(cls):
raise Exception("Unable to create an instance of abstract class %s" %cls)
但是现在,如果我创建一个从F继承的类G,像这样:
class G(F):
pass
然后,我也不能实例化G,因为它调用它的超类的__new__方法。
是否有更好的方法来定义抽象类?
只是对@TimGilbert老派回答的一个快速补充…你可以让你的抽象基类的init()方法抛出一个异常,这将阻止它被实例化,不是吗?
>>> class Abstract(object):
... def __init__(self):
... raise NotImplementedError("You can't instantiate this class!")
...
>>> a = Abstract()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in __init__
NotImplementedError: You can't instantiate this class!
这里有一个不需要处理ABC模块的非常简单的方法。
在你想要成为抽象类的类的__init__方法中,你可以检查self的“类型”。如果self类型是基类,则调用者试图实例化基类,因此引发异常。这里有一个简单的例子:
class Base():
def __init__(self):
if type(self) is Base:
raise Exception('Base is an abstract class and cannot be instantiated directly')
# Any initialization code
print('In the __init__ method of the Base class')
class Sub(Base):
def __init__(self):
print('In the __init__ method of the Sub class before calling __init__ of the Base class')
super().__init__()
print('In the __init__ method of the Sub class after calling __init__ of the Base class')
subObj = Sub()
baseObj = Base()
当运行时,它产生:
In the __init__ method of the Sub class before calling __init__ of the Base class
In the __init__ method of the Base class
In the __init__ method of the Sub class after calling __init__ of the Base class
Traceback (most recent call last):
File "/Users/irvkalb/Desktop/Demo files/Abstract.py", line 16, in <module>
baseObj = Base()
File "/Users/irvkalb/Desktop/Demo files/Abstract.py", line 4, in __init__
raise Exception('Base is an abstract class and cannot be instantiated directly')
Exception: Base is an abstract class and cannot be instantiated directly
这表明您可以实例化继承自基类的子类,但不能直接实例化基类。