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# (C) Copyright 2005-2023 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!
import unittest
from traits.api import HasTraits, Str, Instance, Any
class TestEventOrder(unittest.TestCase):
""" Tests that demonstrate that trait events are delivered in LIFO
order rather than FIFO order.
Baz receives the "effect" event before it receives the "cause" event.
"""
def test_lifo_order(self):
foo = Foo(cause="ORIGINAL")
bar = Bar(foo=foo, test=self)
# flake8 complains about unused "baz", but we need to keep it
# alive for listeners to fire.
baz = Baz(bar=bar, test=self) # noqa: F841
self.events_delivered = []
foo.cause = "CHANGE"
lifo = [
"Bar._caused_changed",
"Baz._effect_changed",
"Baz._caused_changed",
]
self.assertEqual(self.events_delivered, lifo)
class Foo(HasTraits):
cause = Str
class Bar(HasTraits):
foo = Instance(Foo)
effect = Str
test = Any
def _foo_changed(self, obj, old, new):
if old is not None and old is not new:
old.on_trait_change(self._cause_changed, name="cause", remove=True)
if new is not None:
new.on_trait_change(self._cause_changed, name="cause")
def _cause_changed(self, obj, name, old, new):
self.test.events_delivered.append("Bar._caused_changed")
self.effect = new.lower()
class Baz(HasTraits):
bar = Instance(Bar)
test = Any
def _bar_changed(self, obj, old, new):
if old is not None and old is not new:
old.on_trait_change(
self._effect_changed, name="effect", remove=True
)
old.foo.on_trait_change(
self._cause_changed, name="cause", remove=True
)
if new is not None:
new.foo.on_trait_change(self._cause_changed, name="cause")
new.on_trait_change(self._effect_changed, name="effect")
def _cause_changed(self, obj, name, old, new):
self.test.events_delivered.append("Baz._caused_changed")
def _effect_changed(self, obj, name, old, new):
self.test.events_delivered.append("Baz._effect_changed")
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