Creating descriptors

A descriptor is a class that mediates attribute access. The descriptor class can be used to get, set, or delete attribute values. Descriptor objects are built inside a class at class definition time.

The descriptor design pattern has two parts: an owner class and the attribute descriptor itself. The owner class uses one or more descriptors for its attributes. A descriptor class defines some combination of get, set, and delete methods. An instance of the descriptor class will be an attribute of the owner class.

Properties are based on the method functions of the owner class. A descriptor, unlike a property, is an instance of a class different from the owning class. Therefore, descriptors are often reusable, generic kinds of attributes. The owning class can have multiple instances of each descriptor class to manage attributes with similar behaviors.

Unlike other attributes, descriptors are created at the class level. They're not created within the __init__() initialization...