Class enthought.​traits.​trait_handlers.​TraitType

Base class for new trait types.

This class enables you to define new traits using a class-based approach, instead of by calling the Trait() factory function with an instance of a TraitHandler derived object.

When subclassing this class, you can implement one or more of the method signatures below. Note that these methods are defined only as comments, because the absence of method definitions in the subclass definition implicitly provides information about how the trait should operate.

The optional methods are as follows:

• get ( self, object, name ):

  This is the getter method of a trait that behaves like a property.

  Parameters

  object : an object

  The object that the property applies to.

  name : string

  The name of the property on object property.

  Description

  If neither this method nor the set() method is defined, the value of the trait is handled like a normal object attribute. If this method is not defined, but the set() method is defined, the trait behaves like a write-only property. This method should return the value of the name property for the object object.

• set ( self, object, name, value )

  This is the setter method of a trait that behaves like a property.

  Parameters

  object : instance

  The object that the property applies to.

  name : string

  The name of the property on object.

  value : any

  The value being assigned as the value of the property.

  Description

  If neither this method nor the get() method is implemented, the trait behaves like a normal trait attribute. If this method is not defined, but the get() method is defined, the trait behaves like a read-only property. This method does not need to return a value, but it should raise a TraitError exception if the specified value is not valid and cannot be coerced or adapted to a valid value.

• validate ( self, object, name, value )

  This method validates, coerces, or adapts the specified value as the value of the name trait of the object object. This method is called when a value is assigned to an object trait that is based on this subclass of TraitType and the class does not contain a definition for either the get() or set() methods. This method must return the original value or any suitably coerced or adapted value that is a legal value for the trait. If value is not a legal value for the trait, and cannot be coerced or adapted to a legal value, the method should either raise a TraitError or call the error method to raise the TraitError on its behalf.

• is_valid_for ( self, value )

  As an alternative to implementing the validate method, you can instead implement the is_valid_for method, which receives only the value being assigned. It should return True if the value is valid, and False otherwise.

• value_for ( self, value )

  As another alternative to implementing the validate method, you can instead implement the value_for method, which receives only the value being assigned. It should return the validated form of value if it is valid, or raise a TraitError if the value is not valid.

• post_setattr ( self, object, name, value )

  This method allows the trait to do additional processing after value has been successfully assigned to the name trait of the object object. For most traits there is no additional processing that needs to be done, and this method need not be defined. It is normally used for creating "shadow" (i.e., "mapped" traits), but other uses may arise as well. This method does not need to return a value, and should normally not raise any exceptions.