dirtybitcode.py

class TraitedSpec2(traits.HasTraits):
    trigger = traits.Event
    hashval = traits.Property(depends_on='trigger')
    
    @traits.cached_property
    def _get_hashval(self):
        print "calc hash"
        import numpy as np
        return np.random.random()
    
    def _anytrait_changed(self, name):
        if name in ['trait_added', 'trait_modified', 'hashval', 'trigger']:
            return
        self.trigger = True

class TraitedSpec3(traits.HasTraits):
    trigger = traits.Event
    hashval = traits.Property(depends_on='trigger')
    
    @traits.cached_property
    def _get_hashval(self):
        print "calc hash"
        import numpy as np
        return np.random.random()

    @traits.on_trait_change('*')
    def foo_changed(self, name):
        if name != 'trigger':
            self.trigger = True

spec2.py

In [16]: class foo(nib.TraitedSpec2):
    goo = nib.traits.Float

In [18]: a = foo()

In [19]: a.hashval
calc hash
Out[19]: 0.3683029010095128

In [20]: a.hashval
Out[20]: 0.3683029010095128

In [21]: a.goo = 1.1
calc hash

In [22]: a.hashval
Out[22]: 0.047413607727976648

In [23]: a.goo = 1.1

In [24]: a.hashval
Out[24]: 0.047413607727976648

spec3crash.py

In [9]: class foo(nib.TraitedSpec3):
    goo = nib.traits.Float

In [11]: a = foo()

In [12]: a.hashval
calc hash
Out[12]: 0.57163717292479677

In [13]: a.hashval
Out[13]: 0.57163717292479677

In [14]: a.goo = 1.1
Exception occurred in traits notification handler.
Please check the log file for details.
Exception occurred in traits notification handler for object: <__main__.foo object at 0x102bc5290>, trait: goo, old value: 0.0, new value: 1.1
Traceback (most recent call last):
  File "/Library/Python/2.6/site-packages/Traits-3.3.1-py2.6-macosx-10.6-universal.egg/enthought/traits/trait_notifiers.py", line 586, in rebind_call_4
    object, trait_name, old, new )
  File "/Library/Python/2.6/site-packages/Traits-3.3.1-py2.6-macosx-10.6-universal.egg/enthought/traits/trait_notifiers.py", line 424, in dispatch
    handler( *args )
  File "/Library/Python/2.6/site-packages/Traits-3.3.1-py2.6-macosx-10.6-universal.egg/enthought/traits/traits_listener.py", line 474, in handle_dst
    object, name = self.next.register( new )
  File "/Library/Python/2.6/site-packages/Traits-3.3.1-py2.6-macosx-10.6-universal.egg/enthought/traits/traits_listener.py", line 397, in register
    trait = new.base_trait( name )
AttributeError: 'float' object has no attribute 'base_trait'