3.2.3        Attribute-specific Handler Signatures

For an attribute specific notification handler, the method signatures supported are:

_name_changed(self)

_name_changed(self, new)

_name_changed(self, old, new)

_name_changed(self, name, old, new)

The method name can also be _name_fired(), with the same set of signatures.

In these signatures:

·    new is the new value assigned to the trait attribute. For List and Dict objects, this is a list of the items that were added.

·    old is the old value assigned to the trait attribute. For List and Dict objects, this is a list of the items that were deleted.

·    name is the name of the trait attribute.  The extended trait name syntax is not supported.[4]

Note that these signatures follow a different pattern for argument interpretation from dynamic handlers and decorated static handlers. Both of the following methods define a handler for an object’s name trait:

def _name_changed( self, arg1, arg2, arg3):

    pass

@on_trait_change('name')

def some_method( self, arg1, arg2, arg3):

    pass

However, the interpretation of arguments to these methods differs, as shown in Table 6.

Table 6 Handler argument interpretation