# encoding: utf-8 """ Tests for IPython.utils.traitlets. Authors: * Brian Granger * Enthought, Inc. Some of the code in this file comes from enthought.traits and is licensed under the BSD license. Also, many of the ideas also come from enthought.traits even though our implementation is very different. """ #----------------------------------------------------------------------------- # Copyright (C) 2008-2011 The IPython Development Team # # Distributed under the terms of the BSD License. The full license is in # the file COPYING, distributed as part of this software. #----------------------------------------------------------------------------- #----------------------------------------------------------------------------- # Imports #----------------------------------------------------------------------------- import re import sys from unittest import TestCase import nose.tools as nt from nose import SkipTest from IPython.utils.traitlets import ( HasTraits, MetaHasTraits, TraitType, Any, CBytes, Dict, Int, Long, Integer, Float, Complex, Bytes, Unicode, TraitError, Undefined, Type, This, Instance, TCPAddress, List, Tuple, ObjectName, DottedObjectName, CRegExp, link ) from IPython.utils import py3compat from IPython.testing.decorators import skipif #----------------------------------------------------------------------------- # Helper classes for testing #----------------------------------------------------------------------------- class HasTraitsStub(HasTraits): def _notify_trait(self, name, old, new): self._notify_name = name self._notify_old = old self._notify_new = new #----------------------------------------------------------------------------- # Test classes #----------------------------------------------------------------------------- class TestTraitType(TestCase): def test_get_undefined(self): class A(HasTraits): a = TraitType a = A() self.assertEqual(a.a, Undefined) def test_set(self): class A(HasTraitsStub): a = TraitType a = A() a.a = 10 self.assertEqual(a.a, 10) self.assertEqual(a._notify_name, 'a') self.assertEqual(a._notify_old, Undefined) self.assertEqual(a._notify_new, 10) def test_validate(self): class MyTT(TraitType): def validate(self, inst, value): return -1 class A(HasTraitsStub): tt = MyTT a = A() a.tt = 10 self.assertEqual(a.tt, -1) def test_default_validate(self): class MyIntTT(TraitType): def validate(self, obj, value): if isinstance(value, int): return value self.error(obj, value) class A(HasTraits): tt = MyIntTT(10) a = A() self.assertEqual(a.tt, 10) # Defaults are validated when the HasTraits is instantiated class B(HasTraits): tt = MyIntTT('bad default') self.assertRaises(TraitError, B) def test_is_valid_for(self): class MyTT(TraitType): def is_valid_for(self, value): return True class A(HasTraits): tt = MyTT a = A() a.tt = 10 self.assertEqual(a.tt, 10) def test_value_for(self): class MyTT(TraitType): def value_for(self, value): return 20 class A(HasTraits): tt = MyTT a = A() a.tt = 10 self.assertEqual(a.tt, 20) def test_info(self): class A(HasTraits): tt = TraitType a = A() self.assertEqual(A.tt.info(), 'any value') def test_error(self): class A(HasTraits): tt = TraitType a = A() self.assertRaises(TraitError, A.tt.error, a, 10) def test_dynamic_initializer(self): class A(HasTraits): x = Int(10) def _x_default(self): return 11 class B(A): x = Int(20) class C(A): def _x_default(self): return 21 a = A() self.assertEqual(a._trait_values, {}) self.assertEqual(list(a._trait_dyn_inits.keys()), ['x']) self.assertEqual(a.x, 11) self.assertEqual(a._trait_values, {'x': 11}) b = B() self.assertEqual(b._trait_values, {'x': 20}) self.assertEqual(list(a._trait_dyn_inits.keys()), ['x']) self.assertEqual(b.x, 20) c = C() self.assertEqual(c._trait_values, {}) self.assertEqual(list(a._trait_dyn_inits.keys()), ['x']) self.assertEqual(c.x, 21) self.assertEqual(c._trait_values, {'x': 21}) # Ensure that the base class remains unmolested when the _default # initializer gets overridden in a subclass. a = A() c = C() self.assertEqual(a._trait_values, {}) self.assertEqual(list(a._trait_dyn_inits.keys()), ['x']) self.assertEqual(a.x, 11) self.assertEqual(a._trait_values, {'x': 11}) class TestHasTraitsMeta(TestCase): def test_metaclass(self): self.assertEqual(type(HasTraits), MetaHasTraits) class A(HasTraits): a = Int a = A() self.assertEqual(type(a.__class__), MetaHasTraits) self.assertEqual(a.a,0) a.a = 10 self.assertEqual(a.a,10) class B(HasTraits): b = Int() b = B() self.assertEqual(b.b,0) b.b = 10 self.assertEqual(b.b,10) class C(HasTraits): c = Int(30) c = C() self.assertEqual(c.c,30) c.c = 10 self.assertEqual(c.c,10) def test_this_class(self): class A(HasTraits): t = This() tt = This() class B(A): tt = This() ttt = This() self.assertEqual(A.t.this_class, A) self.assertEqual(B.t.this_class, A) self.assertEqual(B.tt.this_class, B) self.assertEqual(B.ttt.this_class, B) class TestHasTraitsNotify(TestCase): def setUp(self): self._notify1 = [] self._notify2 = [] def notify1(self, name, old, new): self._notify1.append((name, old, new)) def notify2(self, name, old, new): self._notify2.append((name, old, new)) def test_notify_all(self): class A(HasTraits): a = Int b = Float a = A() a.on_trait_change(self.notify1) a.a = 0 self.assertEqual(len(self._notify1),0) a.b = 0.0 self.assertEqual(len(self._notify1),0) a.a = 10 self.assertTrue(('a',0,10) in self._notify1) a.b = 10.0 self.assertTrue(('b',0.0,10.0) in self._notify1) self.assertRaises(TraitError,setattr,a,'a','bad string') self.assertRaises(TraitError,setattr,a,'b','bad string') self._notify1 = [] a.on_trait_change(self.notify1,remove=True) a.a = 20 a.b = 20.0 self.assertEqual(len(self._notify1),0) def test_notify_one(self): class A(HasTraits): a = Int b = Float a = A() a.on_trait_change(self.notify1, 'a') a.a = 0 self.assertEqual(len(self._notify1),0) a.a = 10 self.assertTrue(('a',0,10) in self._notify1) self.assertRaises(TraitError,setattr,a,'a','bad string') def test_subclass(self): class A(HasTraits): a = Int class B(A): b = Float b = B() self.assertEqual(b.a,0) self.assertEqual(b.b,0.0) b.a = 100 b.b = 100.0 self.assertEqual(b.a,100) self.assertEqual(b.b,100.0) def test_notify_subclass(self): class A(HasTraits): a = Int class B(A): b = Float b = B() b.on_trait_change(self.notify1, 'a') b.on_trait_change(self.notify2, 'b') b.a = 0 b.b = 0.0 self.assertEqual(len(self._notify1),0) self.assertEqual(len(self._notify2),0) b.a = 10 b.b = 10.0 self.assertTrue(('a',0,10) in self._notify1) self.assertTrue(('b',0.0,10.0) in self._notify2) def test_static_notify(self): class A(HasTraits): a = Int _notify1 = [] def _a_changed(self, name, old, new): self._notify1.append((name, old, new)) a = A() a.a = 0 # This is broken!!! self.assertEqual(len(a._notify1),0) a.a = 10 self.assertTrue(('a',0,10) in a._notify1) class B(A): b = Float _notify2 = [] def _b_changed(self, name, old, new): self._notify2.append((name, old, new)) b = B() b.a = 10 b.b = 10.0 self.assertTrue(('a',0,10) in b._notify1) self.assertTrue(('b',0.0,10.0) in b._notify2) def test_notify_args(self): def callback0(): self.cb = () def callback1(name): self.cb = (name,) def callback2(name, new): self.cb = (name, new) def callback3(name, old, new): self.cb = (name, old, new) class A(HasTraits): a = Int a = A() a.on_trait_change(callback0, 'a') a.a = 10 self.assertEqual(self.cb,()) a.on_trait_change(callback0, 'a', remove=True) a.on_trait_change(callback1, 'a') a.a = 100 self.assertEqual(self.cb,('a',)) a.on_trait_change(callback1, 'a', remove=True) a.on_trait_change(callback2, 'a') a.a = 1000 self.assertEqual(self.cb,('a',1000)) a.on_trait_change(callback2, 'a', remove=True) a.on_trait_change(callback3, 'a') a.a = 10000 self.assertEqual(self.cb,('a',1000,10000)) a.on_trait_change(callback3, 'a', remove=True) self.assertEqual(len(a._trait_notifiers['a']),0) def test_notify_only_once(self): class A(HasTraits): listen_to = ['a'] a = Int(0) b = 0 def __init__(self, **kwargs): super(A, self).__init__(**kwargs) self.on_trait_change(self.listener1, ['a']) def listener1(self, name, old, new): self.b += 1 class B(A): c = 0 d = 0 def __init__(self, **kwargs): super(B, self).__init__(**kwargs) self.on_trait_change(self.listener2) def listener2(self, name, old, new): self.c += 1 def _a_changed(self, name, old, new): self.d += 1 b = B() b.a += 1 self.assertEqual(b.b, b.c) self.assertEqual(b.b, b.d) b.a += 1 self.assertEqual(b.b, b.c) self.assertEqual(b.b, b.d) class TestHasTraits(TestCase): def test_trait_names(self): class A(HasTraits): i = Int f = Float a = A() self.assertEqual(sorted(a.trait_names()),['f','i']) self.assertEqual(sorted(A.class_trait_names()),['f','i']) def test_trait_metadata(self): class A(HasTraits): i = Int(config_key='MY_VALUE') a = A() self.assertEqual(a.trait_metadata('i','config_key'), 'MY_VALUE') def test_traits(self): class A(HasTraits): i = Int f = Float a = A() self.assertEqual(a.traits(), dict(i=A.i, f=A.f)) self.assertEqual(A.class_traits(), dict(i=A.i, f=A.f)) def test_traits_metadata(self): class A(HasTraits): i = Int(config_key='VALUE1', other_thing='VALUE2') f = Float(config_key='VALUE3', other_thing='VALUE2') j = Int(0) a = A() self.assertEqual(a.traits(), dict(i=A.i, f=A.f, j=A.j)) traits = a.traits(config_key='VALUE1', other_thing='VALUE2') self.assertEqual(traits, dict(i=A.i)) # This passes, but it shouldn't because I am replicating a bug in # traits. traits = a.traits(config_key=lambda v: True) self.assertEqual(traits, dict(i=A.i, f=A.f, j=A.j)) def test_init(self): class A(HasTraits): i = Int() x = Float() a = A(i=1, x=10.0) self.assertEqual(a.i, 1) self.assertEqual(a.x, 10.0) def test_positional_args(self): class A(HasTraits): i = Int(0) def __init__(self, i): super(A, self).__init__() self.i = i a = A(5) self.assertEqual(a.i, 5) # should raise TypeError if no positional arg given self.assertRaises(TypeError, A) #----------------------------------------------------------------------------- # Tests for specific trait types #----------------------------------------------------------------------------- class TestType(TestCase): def test_default(self): class B(object): pass class A(HasTraits): klass = Type a = A() self.assertEqual(a.klass, None) a.klass = B self.assertEqual(a.klass, B) self.assertRaises(TraitError, setattr, a, 'klass', 10) def test_value(self): class B(object): pass class C(object): pass class A(HasTraits): klass = Type(B) a = A() self.assertEqual(a.klass, B) self.assertRaises(TraitError, setattr, a, 'klass', C) self.assertRaises(TraitError, setattr, a, 'klass', object) a.klass = B def test_allow_none(self): class B(object): pass class C(B): pass class A(HasTraits): klass = Type(B, allow_none=False) a = A() self.assertEqual(a.klass, B) self.assertRaises(TraitError, setattr, a, 'klass', None) a.klass = C self.assertEqual(a.klass, C) def test_validate_klass(self): class A(HasTraits): klass = Type('no strings allowed') self.assertRaises(ImportError, A) class A(HasTraits): klass = Type('rub.adub.Duck') self.assertRaises(ImportError, A) def test_validate_default(self): class B(object): pass class A(HasTraits): klass = Type('bad default', B) self.assertRaises(ImportError, A) class C(HasTraits): klass = Type(None, B, allow_none=False) self.assertRaises(TraitError, C) def test_str_klass(self): class A(HasTraits): klass = Type('IPython.utils.ipstruct.Struct') from IPython.utils.ipstruct import Struct a = A() a.klass = Struct self.assertEqual(a.klass, Struct) self.assertRaises(TraitError, setattr, a, 'klass', 10) class TestInstance(TestCase): def test_basic(self): class Foo(object): pass class Bar(Foo): pass class Bah(object): pass class A(HasTraits): inst = Instance(Foo) a = A() self.assertTrue(a.inst is None) a.inst = Foo() self.assertTrue(isinstance(a.inst, Foo)) a.inst = Bar() self.assertTrue(isinstance(a.inst, Foo)) self.assertRaises(TraitError, setattr, a, 'inst', Foo) self.assertRaises(TraitError, setattr, a, 'inst', Bar) self.assertRaises(TraitError, setattr, a, 'inst', Bah()) def test_unique_default_value(self): class Foo(object): pass class A(HasTraits): inst = Instance(Foo,(),{}) a = A() b = A() self.assertTrue(a.inst is not b.inst) def test_args_kw(self): class Foo(object): def __init__(self, c): self.c = c class Bar(object): pass class Bah(object): def __init__(self, c, d): self.c = c; self.d = d class A(HasTraits): inst = Instance(Foo, (10,)) a = A() self.assertEqual(a.inst.c, 10) class B(HasTraits): inst = Instance(Bah, args=(10,), kw=dict(d=20)) b = B() self.assertEqual(b.inst.c, 10) self.assertEqual(b.inst.d, 20) class C(HasTraits): inst = Instance(Foo) c = C() self.assertTrue(c.inst is None) def test_bad_default(self): class Foo(object): pass class A(HasTraits): inst = Instance(Foo, allow_none=False) self.assertRaises(TraitError, A) def test_instance(self): class Foo(object): pass def inner(): class A(HasTraits): inst = Instance(Foo()) self.assertRaises(TraitError, inner) class TestThis(TestCase): def test_this_class(self): class Foo(HasTraits): this = This f = Foo() self.assertEqual(f.this, None) g = Foo() f.this = g self.assertEqual(f.this, g) self.assertRaises(TraitError, setattr, f, 'this', 10) def test_this_inst(self): class Foo(HasTraits): this = This() f = Foo() f.this = Foo() self.assertTrue(isinstance(f.this, Foo)) def test_subclass(self): class Foo(HasTraits): t = This() class Bar(Foo): pass f = Foo() b = Bar() f.t = b b.t = f self.assertEqual(f.t, b) self.assertEqual(b.t, f) def test_subclass_override(self): class Foo(HasTraits): t = This() class Bar(Foo): t = This() f = Foo() b = Bar() f.t = b self.assertEqual(f.t, b) self.assertRaises(TraitError, setattr, b, 't', f) class TraitTestBase(TestCase): """A best testing class for basic trait types.""" def assign(self, value): self.obj.value = value def coerce(self, value): return value def test_good_values(self): if hasattr(self, '_good_values'): for value in self._good_values: self.assign(value) self.assertEqual(self.obj.value, self.coerce(value)) def test_bad_values(self): if hasattr(self, '_bad_values'): for value in self._bad_values: try: self.assertRaises(TraitError, self.assign, value) except AssertionError: assert False, value def test_default_value(self): if hasattr(self, '_default_value'): self.assertEqual(self._default_value, self.obj.value) def tearDown(self): # restore default value after tests, if set if hasattr(self, '_default_value'): self.obj.value = self._default_value class AnyTrait(HasTraits): value = Any class AnyTraitTest(TraitTestBase): obj = AnyTrait() _default_value = None _good_values = [10.0, 'ten', u'ten', [10], {'ten': 10},(10,), None, 1j] _bad_values = [] class IntTrait(HasTraits): value = Int(99) class TestInt(TraitTestBase): obj = IntTrait() _default_value = 99 _good_values = [10, -10] _bad_values = ['ten', u'ten', [10], {'ten': 10},(10,), None, 1j, 10.1, -10.1, '10L', '-10L', '10.1', '-10.1', u'10L', u'-10L', u'10.1', u'-10.1', '10', '-10', u'10', u'-10'] if not py3compat.PY3: _bad_values.extend([long(10), long(-10), 10*sys.maxint, -10*sys.maxint]) class LongTrait(HasTraits): value = Long(99 if py3compat.PY3 else long(99)) class TestLong(TraitTestBase): obj = LongTrait() _default_value = 99 if py3compat.PY3 else long(99) _good_values = [10, -10] _bad_values = ['ten', u'ten', [10], {'ten': 10},(10,), None, 1j, 10.1, -10.1, '10', '-10', '10L', '-10L', '10.1', '-10.1', u'10', u'-10', u'10L', u'-10L', u'10.1', u'-10.1'] if not py3compat.PY3: # maxint undefined on py3, because int == long _good_values.extend([long(10), long(-10), 10*sys.maxint, -10*sys.maxint]) _bad_values.extend([[long(10)], (long(10),)]) @skipif(py3compat.PY3, "not relevant on py3") def test_cast_small(self): """Long casts ints to long""" self.obj.value = 10 self.assertEqual(type(self.obj.value), long) class IntegerTrait(HasTraits): value = Integer(1) class TestInteger(TestLong): obj = IntegerTrait() _default_value = 1 def coerce(self, n): return int(n) @skipif(py3compat.PY3, "not relevant on py3") def test_cast_small(self): """Integer casts small longs to int""" if py3compat.PY3: raise SkipTest("not relevant on py3") self.obj.value = long(100) self.assertEqual(type(self.obj.value), int) class FloatTrait(HasTraits): value = Float(99.0) class TestFloat(TraitTestBase): obj = FloatTrait() _default_value = 99.0 _good_values = [10, -10, 10.1, -10.1] _bad_values = ['ten', u'ten', [10], {'ten': 10},(10,), None, 1j, '10', '-10', '10L', '-10L', '10.1', '-10.1', u'10', u'-10', u'10L', u'-10L', u'10.1', u'-10.1'] if not py3compat.PY3: _bad_values.extend([long(10), long(-10)]) class ComplexTrait(HasTraits): value = Complex(99.0-99.0j) class TestComplex(TraitTestBase): obj = ComplexTrait() _default_value = 99.0-99.0j _good_values = [10, -10, 10.1, -10.1, 10j, 10+10j, 10-10j, 10.1j, 10.1+10.1j, 10.1-10.1j] _bad_values = [u'10L', u'-10L', 'ten', [10], {'ten': 10},(10,), None] if not py3compat.PY3: _bad_values.extend([long(10), long(-10)]) class BytesTrait(HasTraits): value = Bytes(b'string') class TestBytes(TraitTestBase): obj = BytesTrait() _default_value = b'string' _good_values = [b'10', b'-10', b'10L', b'-10L', b'10.1', b'-10.1', b'string'] _bad_values = [10, -10, 10.1, -10.1, 1j, [10], ['ten'],{'ten': 10},(10,), None, u'string'] if not py3compat.PY3: _bad_values.extend([long(10), long(-10)]) class UnicodeTrait(HasTraits): value = Unicode(u'unicode') class TestUnicode(TraitTestBase): obj = UnicodeTrait() _default_value = u'unicode' _good_values = ['10', '-10', '10L', '-10L', '10.1', '-10.1', '', u'', 'string', u'string', u"€"] _bad_values = [10, -10, 10.1, -10.1, 1j, [10], ['ten'], [u'ten'], {'ten': 10},(10,), None] if not py3compat.PY3: _bad_values.extend([long(10), long(-10)]) class ObjectNameTrait(HasTraits): value = ObjectName("abc") class TestObjectName(TraitTestBase): obj = ObjectNameTrait() _default_value = "abc" _good_values = ["a", "gh", "g9", "g_", "_G", u"a345_"] _bad_values = [1, "", u"€", "9g", "!", "#abc", "aj@", "a.b", "a()", "a[0]", object(), object] if sys.version_info[0] < 3: _bad_values.append(u"þ") else: _good_values.append(u"þ") # þ=1 is valid in Python 3 (PEP 3131). class DottedObjectNameTrait(HasTraits): value = DottedObjectName("a.b") class TestDottedObjectName(TraitTestBase): obj = DottedObjectNameTrait() _default_value = "a.b" _good_values = ["A", "y.t", "y765.__repr__", "os.path.join", u"os.path.join"] _bad_values = [1, u"abc.€", "_.@", ".", ".abc", "abc.", ".abc."] if sys.version_info[0] < 3: _bad_values.append(u"t.þ") else: _good_values.append(u"t.þ") class TCPAddressTrait(HasTraits): value = TCPAddress() class TestTCPAddress(TraitTestBase): obj = TCPAddressTrait() _default_value = ('127.0.0.1',0) _good_values = [('localhost',0),('192.168.0.1',1000),('www.google.com',80)] _bad_values = [(0,0),('localhost',10.0),('localhost',-1)] class ListTrait(HasTraits): value = List(Int) class TestList(TraitTestBase): obj = ListTrait() _default_value = [] _good_values = [[], [1], list(range(10))] _bad_values = [10, [1,'a'], 'a', (1,2)] class LenListTrait(HasTraits): value = List(Int, [0], minlen=1, maxlen=2) class TestLenList(TraitTestBase): obj = LenListTrait() _default_value = [0] _good_values = [[1], list(range(2))] _bad_values = [10, [1,'a'], 'a', (1,2), [], list(range(3))] class TupleTrait(HasTraits): value = Tuple(Int) class TestTupleTrait(TraitTestBase): obj = TupleTrait() _default_value = None _good_values = [(1,), None,(0,)] _bad_values = [10, (1,2), [1],('a'), ()] def test_invalid_args(self): self.assertRaises(TypeError, Tuple, 5) self.assertRaises(TypeError, Tuple, default_value='hello') t = Tuple(Int, CBytes, default_value=(1,5)) class LooseTupleTrait(HasTraits): value = Tuple((1,2,3)) class TestLooseTupleTrait(TraitTestBase): obj = LooseTupleTrait() _default_value = (1,2,3) _good_values = [(1,), None, (0,), tuple(range(5)), tuple('hello'), ('a',5), ()] _bad_values = [10, 'hello', [1], []] def test_invalid_args(self): self.assertRaises(TypeError, Tuple, 5) self.assertRaises(TypeError, Tuple, default_value='hello') t = Tuple(Int, CBytes, default_value=(1,5)) class MultiTupleTrait(HasTraits): value = Tuple(Int, Bytes, default_value=[99,b'bottles']) class TestMultiTuple(TraitTestBase): obj = MultiTupleTrait() _default_value = (99,b'bottles') _good_values = [(1,b'a'), (2,b'b')] _bad_values = ((),10, b'a', (1,b'a',3), (b'a',1), (1, u'a')) class CRegExpTrait(HasTraits): value = CRegExp(r'') class TestCRegExp(TraitTestBase): def coerce(self, value): return re.compile(value) obj = CRegExpTrait() _default_value = re.compile(r'') _good_values = [r'\d+', re.compile(r'\d+')] _bad_values = [r'(', None, ()] class DictTrait(HasTraits): value = Dict() def test_dict_assignment(): d = dict() c = DictTrait() c.value = d d['a'] = 5 nt.assert_equal(d, c.value) nt.assert_true(c.value is d) class TestLink(TestCase): def test_connect_same(self): """Verify two traitlets of the same type can be linked together using link.""" # Create two simple classes with Int traitlets. class A(HasTraits): value = Int() a = A(value=9) b = A(value=8) # Conenct the two classes. c = link((a, 'value'), (b, 'value')) # Make sure the values are the same at the point of linking. self.assertEqual(a.value, b.value) # Change one of the values to make sure they stay in sync. a.value = 5 self.assertEqual(a.value, b.value) b.value = 6 self.assertEqual(a.value, b.value) def test_link_different(self): """Verify two traitlets of different types can be linked together using link.""" # Create two simple classes with Int traitlets. class A(HasTraits): value = Int() class B(HasTraits): count = Int() a = A(value=9) b = B(count=8) # Conenct the two classes. c = link((a, 'value'), (b, 'count')) # Make sure the values are the same at the point of linking. self.assertEqual(a.value, b.count) # Change one of the values to make sure they stay in sync. a.value = 5 self.assertEqual(a.value, b.count) b.count = 4 self.assertEqual(a.value, b.count) def test_unlink(self): """Verify two linked traitlets can be unlinked.""" # Create two simple classes with Int traitlets. class A(HasTraits): value = Int() a = A(value=9) b = A(value=8) # Connect the two classes. c = link((a, 'value'), (b, 'value')) a.value = 4 c.unlink() # Change one of the values to make sure they don't stay in sync. a.value = 5 self.assertNotEqual(a.value, b.value) def test_callbacks(self): """Verify two linked traitlets have their callbacks called once.""" # Create two simple classes with Int traitlets. class A(HasTraits): value = Int() class B(HasTraits): count = Int() a = A(value=9) b = B(count=8) # Register callbacks that count. callback_count = [] def a_callback(name, old, new): callback_count.append('a') a.on_trait_change(a_callback, 'value') def b_callback(name, old, new): callback_count.append('b') b.on_trait_change(b_callback, 'count') # Connect the two classes. c = link((a, 'value'), (b, 'count')) # Make sure b's count was set to a's value once. self.assertEqual(''.join(callback_count), 'b') del callback_count[:] # Make sure a's value was set to b's count once. b.count = 5 self.assertEqual(''.join(callback_count), 'ba') del callback_count[:] # Make sure b's count was set to a's value once. a.value = 4 self.assertEqual(''.join(callback_count), 'ab') del callback_count[:]