Add 'indexing-exception' warning, which detects that indexing an exception occurs in Python 2 (behaviour removed in Python 3)

4 files changed, 39 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 8bb3ba9..e40459d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,9 @@ ChangeLog for Pylint
     * Extend the checking for unbalanced-tuple-unpacking and
       unpacking-non-sequence to instance attribute unpacking as well.
 
+    * Add 'indexing-exception' warning, which detects that indexing
+      an exception occurs in Python 2 (behaviour removed in Python 3).
+
 2014-04-18  --  1.2.0
     * Pass the current python paths to pylint process when invoked via
       epylint.  Fixes BitBucket issue #133.
diff --git a/checkers/exceptions.py b/checkers/exceptions.py
index 64aca5b..84f92ea 100644
--- a/checkers/exceptions.py
+++ b/checkers/exceptions.py
@@ -107,6 +107,11 @@ MSGS = {
               'clauses. '
               'See http://www.python.org/dev/peps/pep-3110/',
               {'maxversion': (3, 0)}),
+    'W0713': ('Indexing exceptions will not work on Python 3',
+              'indexing-exception',
+              'Indexing exceptions will not work on Python 3. Use '
+              '`exception.args[index]` instead.',
+              {'maxversion': (3, 0)}),
     }
 
 
@@ -211,6 +216,17 @@ class ExceptionsChecker(BaseChecker):
         if isinstance(node.name, (astroid.Tuple, astroid.List)):
             self.add_message('unpacking-in-except', node=node)
 
+    @check_messages('indexing-exception')
+    def visit_subscript(self, node):
+        """ Look for indexing exceptions. """
+        try:
+            for infered in node.value.infer():
+                if not isinstance(infered, astroid.Instance):
+                    continue
+                if inherit_from_std_ex(infered):
+                    self.add_message('indexing-exception', node=node)
+        except astroid.InferenceError:
+            return
 
     @check_messages('bare-except', 'broad-except', 'pointless-except',
                     'binary-op-exception', 'bad-except-order',
diff --git a/test/input/func_indexing_exceptions_py_30.py b/test/input/func_indexing_exceptions_py_30.py
new file mode 100644
index 0000000..1200631
--- /dev/null
+++ b/test/input/func_indexing_exceptions_py_30.py
@@ -0,0 +1,16 @@
+"""
+Check for indexing exceptions.
+"""
+# pylint: disable=import-error
+__revision__ = 0
+import socket
+from unknown import ExtensionException
+
+class SubException(IndexError):
+    """ empty """
+
+_ = IndexError("test")[0]
+_ = ZeroDivisionError("error")[0]
+_ = ExtensionException("error")[0]
+_ = SubException("error")[1]
+_ = socker.error("socket")[0]
diff --git a/test/messages/func_indexing_exceptions_py_30.txt b/test/messages/func_indexing_exceptions_py_30.txt
new file mode 100644
index 0000000..1ec5412
--- /dev/null
+++ b/test/messages/func_indexing_exceptions_py_30.txt
@@ -0,0 +1,4 @@
+W: 13: Indexing exceptions will not work on Python 3

+W: 14: Indexing exceptions will not work on Python 3

+W: 16: Indexing exceptions will not work on Python 3

+W: 17: Indexing exceptions will not work on Python 3
\ No newline at end of file