bad_property.py

from traits.api import HasTraits, Property, Dict, cached_property, Any, Str, Int


class MyTraits(HasTraits):

    a = Any

    b = Property(Dict(key_trait=Str, value_trait=Int), depends_on=['a'])

    @cached_property
    def _get_b(self):
        return {'a': self.a}


if __name__ == '__main__':
    mt = MyTraits(a='hello')
    print mt.b

Only trait setters are validated, getters are not:

from traits.api import HasTraits, Property, Dict, cached_property, Any, Str, Int, CInt


class MyTraits(HasTraits):

    a = Any

    b = Property(CInt, depends_on=['a'])

    #@cached_property
    def _get_b(self):
        return {'a': self.a}

    def _set_b(self, value):
        print value



if __name__ == '__main__':
    mt = MyTraits(a='hello')
    print mt.b
    mt.b = '12'
    mt.b = 'a12'