[].extend and similar builtin operations don't emit `dict-*-not-iterating` with the Python 3 porting checker

Close #2187

3 files changed, 20 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 27a01eb65..2c19bff86 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -23,6 +23,10 @@ Release date: |TBA|
 
       Close #2042
 
+    * [].extend and similar builtin operations don't emit `dict-*-not-iterating` with the Python 3 porting checker
+
+      Close #2187
+
 
 What's New in Pylint 1.9.2?
 ===========================
diff --git a/pylint/checkers/python3.py b/pylint/checkers/python3.py
index 07052860c..7f04c182c 100644
--- a/pylint/checkers/python3.py
+++ b/pylint/checkers/python3.py
@@ -80,6 +80,11 @@ def _is_builtin(node):
 _ACCEPTS_ITERATOR = {'iter', 'list', 'tuple', 'sorted', 'set', 'sum', 'any',
                      'all', 'enumerate', 'dict', 'filter', 'reversed',
                      'max', 'min'}
+_BUILTIN_METHOD_ACCEPTS_ITERATOR = {
+    'builtins.list.extend',
+    'builtins.dict.update',
+    'builtins.set.update',
+}
 DICT_METHODS = {'items', 'keys', 'values'}
 
 
@@ -109,6 +114,14 @@ def _in_iterating_context(node):
         elif isinstance(parent.func, astroid.Attribute):
             if parent.func.attrname == 'join':
                 return True
+            try:
+                inferred = next(parent.func.infer())
+            except astroid.InferenceError:
+                pass
+            else:
+                if inferred is not astroid.Uninferable:
+                    if inferred.qname() in _BUILTIN_METHOD_ACCEPTS_ITERATOR:
+                        return True
     # If the call is in an unpacking, there's no need to warn,
     # since it can be considered iterating.
     elif (isinstance(parent, astroid.Assign) and
diff --git a/pylint/test/unittest_checker_python3.py b/pylint/test/unittest_checker_python3.py
index ccf1293ea..ee0db32d2 100644
--- a/pylint/test/unittest_checker_python3.py
+++ b/pylint/test/unittest_checker_python3.py
@@ -208,6 +208,9 @@ class TestPython3Checker(testutils.CheckerTestCase):
             'max({}())',
             'min({}())',
             '3 in {}()',
+            'set().update({}())',
+            '[].extend({}())',
+            '{{}}.update({}())',
         ]
         non_iterating_code = [
             'x = __({}())',