Can python objects have nested properties?

Question

I have an object defined as follows

class a():
    @property
    def prop(self):
        print("hello from object.prop")
        @property
        def prop1(self):
            print("Hello from object.prop.prop")

When I call

>>> obj = a()
>>> obj.prop
hello from object.prop
>>> obj.prop.prop

I get the following traceback error

Traceback (most recent call last):
  File "object_property.py", line 13, in <module>
    a.prop.prop1
AttributeError: 'NoneType' object has no attribute 'prop1'

What I am trying to figure out is if I can define nested properties for objects?

Answer 1

The traceback is because your property doesn't have a return statement, hence it returns NoneType, which obviously can't have attributes of its own. Your property would probably need to return an instance of a different class, that has its own prop attribute. Something like this:

class a():
    def __init__(self):
        self.b = b()
    @property
    def prop(self):
        print("hello from object.prop")
        return self.b

class b():
    @property
    def prop(self):
        print("Hello from object.prop.prop")

x = a()
print x.prop.prop
>> hello from object.prop
>> Hello from object.prop.prop
>> None