defaultdict and subclasses of dict are now handled for dict-iter-* checks

Close #2005

4 files changed, 48 insertions, 10 deletions

diff --git a/ChangeLog b/ChangeLog
index 45e018202..8941e8f8b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,10 @@ What's New in Pylint 1.9.0?
 
 Release date:
 
+   * defaultdict and subclasses of dict are now handled for dict-iter-* checks
+
+     Close #2005
+
    * Added a new Python 2/3 check for invalid raise syntax.
 
      Close #1937
diff --git a/doc/whatsnew/1.9.rst b/doc/whatsnew/1.9.rst
index 954a22f20..e71a277d8 100644
--- a/doc/whatsnew/1.9.rst
+++ b/doc/whatsnew/1.9.rst
@@ -47,3 +47,14 @@ New checkers
 
 Other Changes
 =============
+
+* `defaultdict` and subclasses of `dict` are now handled for `dict-iter-*` checks. That
+  means that the following code will now emit warnings for when `iteritems` and friends
+  are accessed:
+
+  .. code-block:: python
+
+      some_dict = defaultdict(list)
+      ...
+      some_dict.iterkeys()
+
diff --git a/pylint/checkers/python3.py b/pylint/checkers/python3.py
index 1556bf0da..315d2d7da 100644
--- a/pylint/checkers/python3.py
+++ b/pylint/checkers/python3.py
@@ -62,8 +62,15 @@ def _check_dict_node(node):
                 inferred_types.add(inferred_node)
     except astroid.InferenceError:
         pass
-    return (not inferred_types
-            or any(isinstance(x, astroid.Dict) for x in inferred_types))
+
+    if not inferred_types:
+        return True
+    for elem in inferred_types:
+        if isinstance(elem, astroid.Dict):
+            return True
+        if isinstance(elem, astroid.Instance) and 'dict' in elem.basenames:
+            return True
+    return False
 
 
 def _is_builtin(node):
diff --git a/pylint/test/unittest_checker_python3.py b/pylint/test/unittest_checker_python3.py
index 98c56e89e..76b8adff7 100644
--- a/pylint/test/unittest_checker_python3.py
+++ b/pylint/test/unittest_checker_python3.py
@@ -384,10 +384,18 @@ class TestPython3Checker(testutils.CheckerTestCase):
                 self.checker.visit_call(node)
 
     def test_dict_iter_method_on_dict(self):
-        node = astroid.extract_node('{}.iterkeys()')
-        message = testutils.Message('dict-iter-method', node=node)
-        with self.assertAddsMessages(message):
-            self.checker.visit_call(node)
+        nodes = astroid.extract_node('''
+        from collections import defaultdict
+        {}.iterkeys() #@
+        defaultdict(list).iterkeys() #@
+        class Someclass(dict):
+            pass
+        Someclass().iterkeys() #@
+        ''')
+        for node in nodes:
+            message = testutils.Message('dict-iter-method', node=node)
+            with self.assertAddsMessages(message):
+                self.checker.visit_call(node)
 
     def test_dict_not_iter_method(self):
         arg_node = astroid.extract_node('x.iterkeys(x)  #@')
@@ -406,10 +414,18 @@ class TestPython3Checker(testutils.CheckerTestCase):
                 self.checker.visit_call(node)
 
     def test_dict_view_method_on_dict(self):
-        node = astroid.extract_node('{}.viewkeys()')
-        message = testutils.Message('dict-view-method', node=node)
-        with self.assertAddsMessages(message):
-            self.checker.visit_call(node)
+        nodes = astroid.extract_node('''
+        from collections import defaultdict
+        {}.viewkeys() #@
+        defaultdict(list).viewkeys() #@
+        class Someclass(dict):
+            pass
+        Someclass().viewkeys() #@
+        ''')
+        for node in nodes:
+            message = testutils.Message('dict-view-method', node=node)
+            with self.assertAddsMessages(message):
+                self.checker.visit_call(node)
 
     def test_dict_not_view_method(self):
         arg_node = astroid.extract_node('x.viewkeys(x)  #@')