def _observer_change_handler(event, graph, handler, target, dispatcher):
""" Handler for maintaining observers. Used by ObserverChangeNotifier.
Parameters
----------
event : DictChangeEvent
Change event that triggers the maintainer.
graph : ObserverGraph
Description for the *downstream* observers, i.e. excluding self.
handler : callable
User handler.
target : object
Object seen by the user as the owner of the observer.
dispatcher : callable
Callable for dispatching the handler.
"""
for removed_item in event.removed.values():
add_or_remove_notifiers(
object=removed_item,
graph=graph,
handler=handler,
target=target,
dispatcher=dispatcher,
remove=True,
)
for added_item in event.added.values():
add_or_remove_notifiers(
object=added_item,
graph=graph,
handler=handler,
target=target,
dispatcher=dispatcher,
remove=False,
)
def observe(object,
expression,
handler,
*,
remove=False,
dispatcher=dispatch_same):
""" Observer or unobserve traits on an object.
Parameters
----------
object : object
An object to be observed. Usually an instance of ``HasTraits``.
expression : ObserverExpression
An object describing what traits are being observed.
handler : callable(event)
User-defined callable to handle change events.
``event`` is an object representing the change.
Its type and content depends on the change.
remove : boolean, optional
If true, remove notifiers. i.e. unobserve the traits.
dispatcher : callable(callable, event)
Callable for dispatching the user-defined handler, i.e. dispatching
callback on a different thread.
"""
# Implicit interface: ``expression`` can be anything with a method
# ``_as_graphs`` that returns a list of ObserverGraph.
for graph in expression._as_graphs():
add_or_remove_notifiers(
object=object,
graph=graph,
handler=handler,
target=object,
dispatcher=dispatcher,
remove=remove,
)
def observer_change_handler(event, graph, handler, target, dispatcher):
""" Handler for maintaining observers.
Parameters
----------
event : TraitChangeEvent
Event triggered by add_trait.
graph : ObserverGraph
Description for the *downstream* observers, i.e. excluding self.
handler : callable
User handler.
target : object
Object seen by the user as the owner of the observer.
dispatcher : callable
Callable for dispatching the handler.
"""
new_graph = ObserverGraph(node=_RestrictedNamedTraitObserver(
name=event.new,
wrapped_observer=graph.node,
),
children=graph.children)
add_or_remove_notifiers(
object=event.object,
graph=new_graph,
handler=handler,
target=target,
dispatcher=dispatcher,
remove=False,
)
def call_add_or_remove_notifiers(**kwargs):
""" Convenience function for calling add_or_remove_notifiers with default
values.
Parameters
----------
**kwargs
New argument values to use instead.
"""
values = dict(
object=mock.Mock(),
graph=ObserverGraph(node=None),
handler=mock.Mock(),
target=_DEFAULT_TARGET,
dispatcher=dispatch_same,
remove=False,
)
values.update(kwargs)
add_or_remove_notifiers(**values)
def observer_change_handler(event, graph, handler, target, dispatcher):
""" Maintain downstream notifiers when the trait changes.
Parameters
----------
event : TraitChangeEvent
The event that triggers this function.
graph : ObserverGraph
Description for the *downstream* observers, i.e. excluding the observer
that contributed this maintainer function.
handler : callable
User handler.
target : object
Object seen by the user as the owner of the observer.
dispatcher : callable
Callable for dispatching the handler.
"""
if event.old not in UNOBSERVABLE_VALUES:
try:
add_or_remove_notifiers(
object=event.old,
graph=graph,
handler=handler,
target=target,
dispatcher=dispatcher,
remove=True,
)
except NotifierNotFound:
# The old value could be a default value that does not have any
# notifier.
pass
if event.new not in UNOBSERVABLE_VALUES:
add_or_remove_notifiers(
object=event.new,
graph=graph,
handler=handler,
target=target,
dispatcher=dispatcher,
remove=False,
)
