Add a new option, 'redefining-builtins-modules'.

The option can be used for controlling the modules
which can redefine builtins, such as six.moves and future.builtins.

Close #464.

2 files changed, 50 insertions, 3 deletions

diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index db03e3a9d..ee2a55792 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -339,7 +339,13 @@ class VariablesChecker(BaseChecker):
                  'help' : 'List of strings which can identify a callback '
                           'function by name. A callback name must start or '
                           'end with one of those strings.'}
-               )
+               ),
+               ("redefining-builtins-modules",
+                {'default': ('six.moves', 'future.builtins'), 'type': 'csv',
+                 'metavar': '<comma separated list>',
+                 'help': 'List of qualified module names which can have objects '
+                         'that can redefine builtins.'}
+               ),
               )
     def __init__(self, linter=None):
         BaseChecker.__init__(self, linter)
@@ -353,7 +359,8 @@ class VariablesChecker(BaseChecker):
         self._to_consume = [(copy(node.locals), {}, 'module')]
         for name, stmts in six.iteritems(node.locals):
             if is_builtin(name) and not is_inside_except(stmts[0]):
-                # do not print Redefining builtin for additional builtins
+                if self._should_ignore_redefined_builtin(stmts[0]):
+                    continue
                 self.add_message('redefined-builtin', args=name, node=stmts[0])
 
     @check_messages('unused-import', 'unused-wildcard-import',
@@ -552,7 +559,8 @@ class VariablesChecker(BaseChecker):
                 if not dummy_rgx.match(name):
                     self.add_message('redefined-outer-name',
                                      args=(name, line), node=stmt)
-            elif is_builtin(name):
+
+            elif is_builtin(name) and not self._should_ignore_redefined_builtin(stmt):
                 # do not print Redefining builtin for additional builtins
                 self.add_message('redefined-builtin', args=name, node=stmt)
 
@@ -737,6 +745,11 @@ class VariablesChecker(BaseChecker):
                     and assign.statement() is not node.statement()):
                 self.add_message('undefined-loop-variable', args=name, node=node)
 
+    def _should_ignore_redefined_builtin(self, stmt):
+        if not isinstance(stmt, astroid.ImportFrom):
+            return False
+        return stmt.modname in self.config.redefining_builtins_modules
+
     @check_messages('redefine-in-handler')
     def visit_excepthandler(self, node):
         for name in get_all_elements(node.name):
diff --git a/pylint/test/unittest_checker_variables.py b/pylint/test/unittest_checker_variables.py
index e42dffcfd..141a34071 100644
--- a/pylint/test/unittest_checker_variables.py
+++ b/pylint/test/unittest_checker_variables.py
@@ -89,6 +89,40 @@ class VariablesCheckerTC(CheckerTestCase):
             self.checker.visit_functiondef(node)
             self.checker.leave_functiondef(node)
 
+    def test_redefined_builtin_ignored(self):
+        node = astroid.parse('''
+        from future.builtins import open
+        ''')
+        with self.assertNoMessages():
+            self.checker.visit_module(node)
+
+    @set_config(redefining_builtins_modules=('os',))
+    def test_redefined_builtin_custom_modules(self):
+        node = astroid.parse('''
+        from os import open
+        ''')
+        with self.assertNoMessages():
+            self.checker.visit_module(node)
+
+    @set_config(redefining_builtins_modules=('os',))
+    def test_redefined_builtin_modname_not_ignored(self):
+        node = astroid.parse('''
+        from future.builtins import open
+        ''')
+        with self.assertAddsMessages(
+                Message('redefined-builtin', node=node.body[0], args='open')):
+            self.checker.visit_module(node)
+
+    @set_config(redefining_builtins_modules=('os',))
+    def test_redefined_builtin_in_function(self):
+        node = test_utils.extract_node('''
+        def test():
+            from os import open
+        ''')
+        with self.assertNoMessages():
+            self.checker.visit_module(node.root())
+            self.checker.visit_functiondef(node)
+
 
 class MissingSubmoduleTest(CheckerTestCase):
     CHECKER_CLASS = variables.VariablesChecker