validate args in traitlets.link, dlink

IPython/utils/tests/test_traitlets.py

@@ -1187,6 +1187,25 b' class TestLink(TestCase):'
         a.value = 4
         self.assertEqual(''.join(callback_count), 'ab')
         del callback_count[:]
+    
+    def test_validate_args(self):
+        class A(HasTraits):
+            value = Int()
+        class B(HasTraits):
+            count = Int()
+        a = A(value=9)
+        b = B(count=8)
+        b.value = 5
+        
+        with self.assertRaises(TypeError):
+            link((a, 'value'))
+        with self.assertRaises(TypeError):
+            link((a, 'value', 'count'), (b, 'count'))
+        with self.assertRaises(TypeError):
+            link((a, 'value'), (b, 'value'))
+        with self.assertRaises(TypeError):
+            link((a, 'traits'), (b, 'count'))
+
 
 class TestDirectionalLink(TestCase):
     def test_connect_same(self):
@@ -1253,6 +1272,25 b' class TestDirectionalLink(TestCase):'
         a.value = 5
         self.assertNotEqual(a.value, b.value)
 
+    def test_validate_args(self):
+        class A(HasTraits):
+            value = Int()
+        class B(HasTraits):
+            count = Int()
+        a = A(value=9)
+        b = B(count=8)
+        b.value = 5
+        
+        with self.assertRaises(TypeError):
+            directional_link((a, 'value'))
+        with self.assertRaises(TypeError):
+            directional_link((a, 'value', 'count'), (b, 'count'))
+        with self.assertRaises(TypeError):
+            directional_link((a, 'value'), (b, 'value'))
+        with self.assertRaises(TypeError):
+            directional_link((a, 'traits'), (b, 'count'))
+
+
 class Pickleable(HasTraits):
     i = Int()
     j = Int()

IPython/utils/traitlets.py

@@ -172,13 +172,24 b' def getmembers(object, predicate=None):'
     results.sort()
     return results
 
+def _validate_link(*tuples):
+    """Validate arguments for traitlet link functions"""
+    for t in tuples:
+        if not len(t) == 2:
+            raise TypeError("Each linked traitlet must be specified as (HasTraits, 'trait_name'), not %r" % t)
+        obj, trait_name = t
+        if not isinstance(obj, HasTraits):
+            raise TypeError("Each object must be HasTraits, not %r" % type(obj))
+        if not trait_name in obj.traits():
+            raise TypeError("%r has no trait %r" % (obj, trait_name))
+
 @skip_doctest
 class link(object):
     """Link traits from different objects together so they remain in sync.
 
     Parameters
     ----------
-    obj : pairs of objects/attributes
+    *args : pairs of objects/attributes
 
     Examples
     --------
@@ -190,6 +201,7 b' class link(object):'
     def __init__(self, *args):
         if len(args) < 2:
             raise TypeError('At least two traitlets must be provided.')
+        _validate_link(*args)
 
         self.objects = {}
 
@@ -245,6 +257,9 b' class directional_link(object):'
     updating = False
 
     def __init__(self, source, *targets):
+        if len(targets) < 1:
+            raise TypeError('At least two traitlets must be provided.')
+        _validate_link(source, *targets)
         self.source = source
         self.targets = targets
 
@@ -276,9 +291,7 b' class directional_link(object):'
         self.source = None
         self.targets = []
 
-def dlink(source, *targets):
-    """Shorter helper function returning a directional_link object"""
-    return directional_link(source, *targets)
+dlink = directional_link
 
 #-----------------------------------------------------------------------------
 # Base TraitType for all traits