Question

我无法运行此代码，因为我得到了异常：

NameError: name 'abstractmethod' is not defined
File "C:\Tests\trunk\PythonTests\AbstractClasses.py", line 12, in <module>
  class MyIterable:
File "C:\Tests\trunk\PythonTests\AbstractClasses.py", line 15, in MyIterable
  @abstractmethod

from abc import ABCMeta

class Foo(object):
    def __getitem__(self, index):
        print '__get_item__ Foo'
    def __len__(self):
        print '__len__ Foo'
    def get_iterator(self):
        print 'get_iterator Foo'
        return iter(self)

class MyIterable:
    __metaclass__ = ABCMeta

    @abstractmethod
    def __iter__(self):
        while False:
            yield None

    def get_iterator(self):
        return self.__iter__()

    @classmethod
    def __subclasshook__(cls, C):
        if cls is MyIterable:
            if any("__iter__" in B.__dict__ for B in C.__mro__):
                print "I'm in __subclasshook__"
                return True
        return NotImplemented

MyIterable.register(Foo)

x=Foo()
x.__subclasshook__()

我确信代码没问题，因为我是从http://docs.python.org/library/abc.html

获得的

修改

感谢您的回答，它现在有效，但为什么

print '__subclasshook__'

这不起作用？我没有进入Debug I / 0

Answer 1

您只导入了ABCMeta

from abc import ABCMeta

还导入abstractmethod

from abc import ABCMeta, abstractmethod

一切都应该没问题。

Answer 2

您需要从abstractmethod导入abc。

Answer 3

您需要将导入ABC更改为ABCMeta

from abc import ABCMeta, abstractmethod

class AbstractClassExample(ABCMeta):

    def __init__(self, value):
        self.value = value
        super().__init__()

    @abstractmethod
    def do_something(self):
        print("do_something")


class DoAdd42(AbstractClassExample):
    print("DoAdd42")

x = DoAdd42(4)

abstractmethod没有定义

3 个答案: