iterate over class properties?

[Gribouillis]

The most important call is add_property_names(A) if you look at what it does in line 18, it adds a new classmethod named property_names to class A. Everything happens as if we had written

class A:
    @classmethod
    def property_names(cls):
        ...

It means that we can now call A.property_names() or A().property_names() or even C.property_names() because C is a subclass of A.

Now look at this method at line 11. It looks in a global dictionary _register
if we have already stored a list of property names _register[A] for class A. If not it computes this list by calling _get_names(A). This way the list of properties is only computed once for each class.

Last subtlety: add_property_names(cls) returns cls. This allows us to use it as a class decorator and write

@add_property_names
class A:
    pass

so that we don't need to call explicitly add_property_names after the definition of class A.