The traits package provides a metaclass with special attributes that are
called traits. A trait is a type definition that can be used for normal
Python object attributes, giving the attributes some additional characteristics:
* Initialization: A trait attribute can have a default value
* Validation: A trait attribute is manifestly typed.
* Delegation: The value of a trait attribute can be contained in another
object
* Notification: Setting the value of a trait attribute can fired
callbacks
* Visualization: With the TraitsUI package, GUIs can be generated
automatically from traited objects.
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