bugfix: Differ now produce correct diff for nested derivatives

example: dict derivative placed in another dict vs. same structure and data
with just dicts are now considered different

nested_diff/__init__.py

@@ -132,7 +132,8 @@ def diff(self, a, b):
 
         This method is a dispatcher and calls registered diff method for each
         diffed values pair according to their type. `diff__default` called for
-        non-registered types. Args and kwargs passed to called method as is.
+        unequal and not registered types. Args and kwargs passed to called
+        method as is.
 
         :param a: First object to diff.
         :param b: Second object to diff.
@@ -156,8 +157,11 @@ def diff(self, a, b):
                 )
 
         if a.__class__ is b.__class__:
-            if a == b:
+            # it's faster to compare pickled dumps and dig differences
+            # afterwards than recursively diff each pair of objects
+            if a is b or dumps(a, -1) == dumps(b, -1):
                 return {'U': a} if self.op_u else {}
+
             return self.get_differ(a.__class__)(a, b)
 
         return self.diff__default(a, b)
@@ -207,13 +211,9 @@ def diff_dict(self, a, b):
                     dif[key] = {'A': b[key]}
                 continue
 
-            if old == new:
-                if self.op_u:
-                    dif[key] = {'U': old}
-            else:
-                subdiff = self.diff(old, new)
-                if subdiff:
-                    dif[key] = subdiff
+            subdiff = self.diff(old, new)
+            if subdiff:
+                dif[key] = subdiff
 
         if dif:
             return {'D': dif}

tests/test_diff.py

@@ -18,3 +18,41 @@ def test_diff(name):
     got = diff(a, b, **opts)
 
     assert expected == got
+
+
+def test_local_objects():
+    def local_function_cant_be_pickled():
+        pass
+
+    a = [local_function_cant_be_pickled]
+    b = []
+
+    with pytest.raises(Exception):  # Can't pickle local object
+        diff(a, b)
+
+
+class SubclassedDict(dict):
+    # can't be declared inside test (Can't pickle local object)
+    pass
+
+
+def test_nested_derivatives():
+    original = {}
+    a = {'k': original}
+    derivative = SubclassedDict()
+    b = {'k': derivative}
+
+    d = diff(a, b)
+
+    assert {'D': {'k': {'N': derivative, 'O': original}}} == d
+
+
+def test_different_object_attributes():
+    a = SubclassedDict()
+    a.arbitrary_attr = True
+    b = SubclassedDict()
+    b.arbitrary_attr = False
+
+    d = diff(a, b)
+
+    assert {'N': b, 'O': a} == d