Abstract attribute (not property)?

Question

What\'s the best practice to define an abstract instance attribute, but not as a property?

I would like to write something like:

class AbstractFoo(me         


        

Answer 1

Just because you define it as an abstractproperty on the abstract base class doesn't mean you have to make a property on the subclass.

e.g. you can:

In [1]: from abc import ABCMeta, abstractproperty

In [2]: class X(metaclass=ABCMeta):
   ...:     @abstractproperty
   ...:     def required(self):
   ...:         raise NotImplementedError
   ...:

In [3]: class Y(X):
   ...:     required = True
   ...:

In [4]: Y()
Out[4]: <__main__.Y at 0x10ae0d390>

If you want to initialise the value in __init__ you can do this:

In [5]: class Z(X):
   ...:     required = None
   ...:     def __init__(self, value):
   ...:         self.required = value
   ...:

In [6]: Z(value=3)
Out[6]: <__main__.Z at 0x10ae15a20>

Since Python 3.3 abstractproperty is deprecated. So Python 3 users should use the following instead:

from abc import ABCMeta, abstractmethod

class X(metaclass=ABCMeta):
    @property
    @abstractmethod
    def required(self):
        raise NotImplementedError