如何在Python中定义抽象类的构造函数实现?

__init__ 抽象方法:

from abc import ABCMeta, abstractmethod

class A(object):
    __metaclass__ = ABCMeta

    @abstractmethod
    def __init__(self, n):
        self.n = n


if __name__ == '__main__':
    a = A(3)

TypeError: Can't instantiate abstract class A with abstract methods __init__

from abc import ABCMeta, abstractmethod

class A(object, metaclass=ABCMeta):

    @abstractmethod
    def __init__(self, n):
        self.n = n


if __name__ == '__main__':
    a = A(3)

同样有效:

TypeError:无法用抽象方法\uu init实例化抽象类A__

class A(object):
  def __init__(self, n):
    if self.__class__ == A:
      raise Exception('I am abstract!')
    self.n = n

用法

class B(A):
  pass
a = A(1)  # Will throw exception
b = B(1)  # Works fine as expected.

__new__ 方法来防止直接实例化。

class A(object):
    __metaclass__ = ABCMeta

    def __new__(cls, *args, **kwargs):
        if cls is A:
            raise TypeError(
                "TypeError: Can't instantiate abstract class {name} directly".format(name=cls.__name__)
            )
        return object.__new__(cls)

输出:

>>> A()
Traceback (most recent call last):
  File "<ipython-input-8-3cd318a12eea>", line 1, in <module>
    A()
  File "/Users/ashwini/py/so.py", line 11, in __new__
    "TypeError: Can't instantiate abstract class {name} directly".format(name=cls.__name__)
TypeError: TypeError: Can't instantiate abstract class A directly

@abc.abstractmethod

您可以实现以下功能:

from abc import ABC
class A(ABC):
    def __init__(self, n):
        self.n = n
        super(A,self).__init__()

我不想让A类被实例化,因为它是一个抽象类。问题是,这实际上是允许的

抽象类是包含一个或多个抽象方法的类。在您的案例代码中,仍然是一个抽象类,它应该提供“抽象类不能实例化”的行为。

i、 e添加decorator@abstractmethod。 以下代码在python 3.6中执行

from abc import ABC, abstractmethod

class Myabs(ABC):

    def __init__(self, connection):
        self.connection = connection
        print("1. calling from base init : {}".format(self.connection))
        super(Myabs, self).__init__()
    @abstractmethod
    def fun1(self, val):
        pass

class D(Myabs):
    def fun1(self, val="hi"):
        print("calling from D: fun1")


object0 = Myabs('connection') # Python 3.6.9

输出: