Description:

The Traits project allows Python programmers to use a special kind of type
definition called a trait which provides object attributes with some
additional characteristics:

* Initialization: A trait has a default value, which is automatically
set as the initial value of an attribute before its first use in a
program.
* Validation: A trait attribute's type is explicitly declared. The
type is evident in the code, and only values that meet a
programmer-specified set of criteria (i.e., the trait definition)
can be assigned to that attribute.
* Delegation: The value of a trait attribute can be contained either
in the defining object or in another object delegated to by the
trait.
* Notification: Setting the value of a trait attribute can notify
other parts of the program that the value has changed.
* Visualization: User interfaces that allow a user to interactively
modify the value of a trait attribute can be automatically
constructed using the trait's definition. (This feature requires
that a supported GUI toolkit be installed. If this feature is not
used, the Traits project does not otherwise require GUI support.)

A class can freely mix trait-based attributes with normal Python
attributes, or can opt to allow the use of only a fixed or open set of
trait attributes within the class. Trait attributes defined by a class
are automatically inherited by any subclass derived from the class.