初始化派生类和抽象类时出现错误

Question

我有这个简单的代码，我得到一个奇怪的错误:

from abc import ABCMeta, abstractmethod
class CVIterator(ABCMeta):
    def __init__(self):
        self.n = None # the value of n is obtained in the fit method
        return

class KFold_new_version(CVIterator): # new version of KFold
    def __init__(self, k):
        assert k > 0, ValueError('cannot have k below 1')
        self.k = k
        return 

cv = KFold_new_version(10)
In [4]: ---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-ec56652b1fdc> in <module>()
----> 1 __pyfile = open('''/tmp/py13196IBS''');exec(compile(__pyfile.read(), '''/home/donbeo/Desktop/prova.py''', 'exec'));__pyfile.close()
/home/donbeo/Desktop/prova.py in <module>()
     19 
     20 
---> 21 cv = KFold_new_version(10)
TypeError: __new__() missing 2 required positional arguments: 'bases' and 'namespace'

我做错了什么?一个理论上的解释将是值得赞赏的。

Answer 1

您错误地使用了ABCMeta元类。它是一个元类，而不是基类。

对于Python 2，这意味着将其分配给类的__metaclass__属性:

class CVIterator(object):
    __metaclass__ = ABCMeta
    def __init__(self):
        self.n = None # the value of n is obtained in the fit method

在Python 3中，在定义类时使用metaclass=...语法:

class CVIterator(metaclass=ABCMeta):
    def __init__(self):
        self.n = None # the value of n is obtained in the fit method

从Python 3.4开始，您可以使用abc.ABC helper类作为基类:

from abc import ABC
class CVIterator(ABC):
    def __init__(self):
        self.n = None # the value of n is obtained in the fit method