Overriding inherited properties’ getters and setters in Python

Question

I’m currently using the @property decorator to achieve “getters and setters” in a couple of my classes. I wish to be able to inherit these @property methods in a child class.

I have some Python code (specifically, I’m working in py3k) which looks vaguely like so:

class A:     @property     def attr(self):         try:             return self._attr         except AttributeError:             return ''  class B(A):     @property     def attr(self):         return A.attr   # The bit that doesn't work.      @attr.setter     def attr(self, value):         self._attr = value  if __name__ == '__main__':     b = B()     print('Before set:', repr(b.attr))     b.attr = 'abc'     print(' After set:', repr(b.attr)) 

I have marked the part that doesn’t work with a comment. I want the base class’ attr getter to be returned. A.attr returns a property object (which is probably very close to what I need!).

Edit:
After receiving the answer below from Ned I thought up what I think is a more elegant solution to this problem.

class A:     @property     def attr(self):         try:             return self._attr         except AttributeError:             return ''  class B(A):             @A.attr.setter     def attr(self, value):         self._attr = value  if __name__ == '__main__':     b = B()     print('Before set:', repr(b.attr))     b.attr = 'abc'     print(' After set:', repr(b.attr)) 

The .setter decorator expects a property object which we can get using @A.attr. This means we do not have to declare the property again in the child class.

(This is the difference between working on a problem at the end of the day vs working on it at the beginning of the day!)

Answer 1

To override a setter in python 2 I did this:

class A(object):     def __init__(self):         self._attr = None      @property     def attr(self):         return self._attr      @attr.setter     def attr(self, value):         self._attr = value   class B(A):     @A.attr.setter     def attr(self, value):         # Do some crazy stuff with `value`         value = value[0:3]         A.attr.fset(self, value) 

To understand where A.attr.fset came from see the documentation on the property class: https://docs.python.org/2/library/functions.html#property

Answer 2

I think you want:

class B(A):     @property     def attr(self):         return super(B, self).attr 

You mention wanting to return the parent class's getter, but you need to invoke the getter, not return it.