Clean Code in Python

Non-data descriptors

We will start with a descriptor that only implements the __get__ method, and see how it is used:

class NonDataDescriptor:    def __get__(self, instance, owner):        if instance is None:            return self        return 42class ClientClass:    descriptor = NonDataDescriptor()

As usual, if we ask for the descriptor, we get the result of its __get__ method:

>>> client = ClientClass()>>> client.descriptor42

But if we change the descriptor attribute to something else, we lose access to this value, and get what was assigned to it instead:

>>> client.descriptor = 43>>> client.descriptor43

Now, if we delete the descriptor, and ask for it again, let's see what we get:

>>> del client.descriptor>>> client.descriptor42

Let's rewind what just happened. When ...