fixes to make Connect pass tests

IPython/utils/tests/test_traitlets.py

@@ -32,7 +32,7 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
+    ObjectName, DottedObjectName, CRegExp, Connect
 )
 from IPython.utils import py3compat
 from IPython.testing.decorators import skipif
@@ -974,11 +974,12 def test_dict_assignment():
     nt.assert_equal(d, c.value)
     nt.assert_true(c.value is d)
 
-def test_connect_same:
+class TestConnect(TestCase):
+    def test_connect_same(self):
     """Verify two traitlets of the same type can be bound together using Connect"""
 
     # Create two simple classes with Int traitlets.
-    class A():
+        class A(HasTraits):
         value = Int()
     a = A(value=9)
     b = A(value=8)
@@ -987,19 +988,19 def test_connect_same:
     c = Connect((a, 'value'), (b, 'value'))
 
     # Make sure the values are the same at the point of connection.
-    assertEqual(a.value, b.value)
+        self.assertEqual(a.value, b.value)
 
     # Change one of the values to make sure they stay in sync.
     a.value = 5
-    assertEqual(a.value, b.value)
+        self.assertEqual(a.value, b.value)
 
-def test_connect_different:
+    def test_connect_different(self):
     """Verify two traitlets of different types can be bound together using Connect"""
 
     # Create two simple classes with Int traitlets.
-    class A():
+        class A(HasTraits):
         value = Int()
-    class B():
+        class B(HasTraits):
         count = Int()
     a = A(value=9)
     b = B(count=8)
@@ -1008,17 +1009,17 def test_connect_different:
     c = Connect((a, 'value'), (b, 'count'))
 
     # Make sure the values are the same at the point of connection.
-    assertEqual(a.value, b.count)
+        self.assertEqual(a.value, b.count)
 
     # Change one of the values to make sure they stay in sync.
     a.value = 5
-    assertEqual(a.value, b.count)
+        self.assertEqual(a.value, b.count)
 
-def test_disconnect:
+    def test_disconnect(self):
     """Verify two connected traitlets can be disconnected"""
 
     # Create two simple classes with Int traitlets.
-    class A():
+        class A(HasTraits):
         value = Int()
     a = A(value=9)
     b = A(value=8)
@@ -1030,4 +1031,4 def test_disconnect:
 
     # Change one of the values to make sure they stay in sync.
     a.value = 5
-    assertNotEqual(a.value, b.value)
  No newline at end of file
+        self.assertNotEqual(a.value, b.value)

IPython/utils/traitlets.py

@@ -199,10 +199,17 class Connect(object):
     """
     updating = False
     def __init__(self, *args):
+        if len(args) < 2:
+            raise TypeError('At least two traitlets must be provided.')
+
         self.objects = args
         for obj,attr in args:
             obj.on_trait_change(self._update, attr)
 
+        # Syncronize the traitlets initially.
+        initial = getattr(args[0][0], args[0][1])
+        self._update(args[0][1], initial, initial)
+
     @contextlib.contextmanager
     def _busy_updating(self):
         self.updating = True