Trait Notification with on_trait_change

See Trait Notification with on_trait_change for details on how to set up change notifications using an older API.

Property depends_on

The depends_on attribute on a Property trait allows change notifications to be fired for the property when one of its dependents has changed. This makes use of on_trait_change internally and therefore this is an older API. See Caching a Property Value for the current API.

For example:

from traits.api import HasStrictTraits, List, Int, Property

class TestScores(HasStrictTraits):

    scores = List(Int)
    average = Property(depends_on='scores')

    def _get_average(self):
        s = self.scores
        return (float(reduce(lambda n1, n2: n1 + n2, s, 0)) / len(s))

The depends_on metadata attribute accepts extended trait references, using the same syntax as the on_trait_change() method’s name parameter, described in The name Parameter. As a result, it can take values that specify attributes on referenced objects, multiple attributes, or attributes that are selected based on their metadata attributes.