traits.base_trait_handler Module¶
Defines the Abstract BaseTraitHandler class.
A trait handler mediates the assignment of values to object traits. It verifies (via its validate() method) that a specified value is consistent with the object trait, and generates a TraitError exception if it is not consistent.
Classes¶
- class traits.base_trait_handler.BaseTraitHandler[source]¶
The task of this class and its subclasses is to verify the correctness of values assigned to object trait attributes.
This class is an alternative to trait validator functions. A trait handler has several advantages over a trait validator function, due to being an object:
Trait handlers have constructors and state. Therefore, you can use them to create parametrized types.
Trait handlers can have multiple methods, whereas validator functions can have only one callable interface. This feature allows more flexibility in their implementation, and allows them to handle a wider range of cases, such as interactions with other components.
- error(object, name, value)[source]¶
Raises a TraitError exception.
This method is called by the validate() method when an assigned value is not valid. Raising a TraitError exception either notifies the user of the problem, or, in the case of compound traits, provides a chance for another trait handler to handle to validate the value.
- full_info(object, name, value)[source]¶
Returns a string describing the type of value accepted by the trait handler.
The string should be a phrase describing the type defined by the TraitHandler subclass, rather than a complete sentence. For example, use the phrase, “a square sprocket” instead of the sentence, “The value must be a square sprocket.” The value returned by full_info() is combined with other information whenever an error occurs and therefore makes more sense to the user if the result is a phrase. The full_info() method is similar in purpose and use to the info attribute of a validator function.
Note that the result can include information specific to the particular trait handler instance. If the full_info() method is not overridden, the default method returns the value of calling the info() method.
- info()[source]¶
Must return a string describing the type of value accepted by the trait handler.
The string should be a phrase describing the type defined by the TraitHandler subclass, rather than a complete sentence. For example, use the phrase, “a square sprocket” instead of the sentence, “The value must be a square sprocket.” The value returned by info() is combined with other information whenever an error occurs and therefore makes more sense to the user if the result is a phrase. The info() method is similar in purpose and use to the info attribute of a validator function.
Note that the result can include information specific to the particular trait handler instance. If the info() method is not overridden, the default method returns the value of the ‘info_text’ attribute.
- get_editor(trait=None)[source]¶
Returns a trait editor that allows the user to modify the trait trait. This method only needs to be specified if traits defined using this trait handler require a non-default trait editor in trait user interfaces. The default implementation of this method returns a trait editor that allows the user to type an arbitrary string as the value.
For more information on trait user interfaces, refer to the Traits UI User Guide.
- Parameters:
trait (Trait) – The trait to be edited.
- inner_traits()[source]¶
Returns a tuple containing the inner traits for this trait. Most trait handlers do not have any inner traits, and so will return an empty tuple. The exceptions are List and Dict trait types, which have inner traits used to validate the values assigned to the trait. For example, in List(Int), the inner traits for List are (Int,).
