[Python]How to create abstract properties in python abstract classes

How to create abstract properties in python abstract classes

In the following code, I create a base abstract class Base. I want all the classes that inherit from Base to provide the name property, so I made this property an @abstractmethod.

Then I created a subclass of Base, called Base_1, which is meant to supply some functionality, but still remain abstract. There is no name property in Base_1, but nevertheless python instatinates an object of that class without an error. How does one create abstract properties?

from abc import ABCMeta, abstractmethod
class Base(object):
    __metaclass__ = ABCMeta
    def __init__(self, strDirConfig):
        self.strDirConfig = strDirConfig

    @abstractmethod
    def _doStuff(self, signals):
        pass

    @property    
    @abstractmethod
    def name(self):
        #this property will be supplied by the inheriting classes
        #individually
        pass


class Base_1(Base):
    __metaclass__ = ABCMeta
    # this class does not provide the name property, should raise an error
    def __init__(self, strDirConfig):
        super(Base_1, self).__init__(strDirConfig)

    def _doStuff(self, signals):
        print 'Base_1 does stuff'


class C(Base_1):
    @property
    def name(self):
        return 'class C'


if __name__ == '__main__':
    b1 = Base_1('abc')  

Until Python 3.3, you cannot nest @abstractmethod and @property.

Use @abstractproperty to create abstract properties (docs).

from abc import ABCMeta, abstractmethod, abstractproperty

class Base(object):
    # ...
    @abstractproperty
    def name(self):
        pass

The code now raises the correct exception:

Traceback (most recent call last):
  File "foo.py", line 36, in 
    b1 = Base_1('abc')  
TypeError: Can't instantiate abstract class Base_1 with abstract methods name

举个小栗子

# -*- coding: utf-8 -*-
from abc import ABCMeta, abstractmethod, abstractproperty
class A:
    __metaclass__ = ABCMeta
    @abstractproperty
    def a(self):
        pass

class B(A):
    __metaclass__ = ABCMeta
    @property
    def a(self):
        return 'property a'
if '__main__' == __name__:
    b = B()
    print b.a