Detect assignments to a loop variable in the else branch of a for statement.

Closes: #9188,#4024

4 files changed, 33 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 9e7ef338f..ca777f241 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -11,6 +11,9 @@ ChangeLog for PyLint
     * #50461, #52020, #51222: Do not issue warnings when using 2.6's
       property.setter/deleter functionality (patch by dneil@google.com)
 
+    * #9188, #4024: Do not trigger W0631 if a loop variable is assigned
+      in the else branch of a for loop.
+
 
 
 2011-10-07  --  0.25.0
diff --git a/checkers/variables.py b/checkers/variables.py
index 14bb1624e..484a9526f 100644
--- a/checkers/variables.py
+++ b/checkers/variables.py
@@ -28,6 +28,12 @@ from pylint.checkers.utils import (PYMETHODS, is_ancestor_name, is_builtin,
      is_defined_before, is_error, is_func_default, is_func_decorator,
      assign_parent, check_messages, is_inside_except, clobber_in_except)
 
+
+def in_for_else_branch(parent, stmt):
+  """Returns True if stmt in inside the else branch for a parent For stmt."""
+  return (isinstance(parent, astng.For) and
+          any(else_stmt.parent_of(stmt) for else_stmt in parent.orelse))
+
 def overridden_method(klass, name):
     """get overridden method if any"""
     try:
@@ -348,7 +354,8 @@ builtins. Remember that you should avoid to define new builtins when possible.'
         else:
             _astmts = astmts[:1]
         for i, stmt in enumerate(astmts[1:]):
-            if astmts[i].statement().parent_of(stmt):
+            if (astmts[i].statement().parent_of(stmt)
+                and not in_for_else_branch(astmts[i].statement(), stmt)):
                 continue
             _astmts.append(stmt)
         astmts = _astmts
diff --git a/test/input/func_w0631.py b/test/input/func_w0631.py
new file mode 100644
index 000000000..2524f5e11
--- /dev/null
+++ b/test/input/func_w0631.py
@@ -0,0 +1,21 @@
+"""Check possible undefined loopvar
+"""
+
+__revision__ = 0
+
+def do_stuff(some_random_list):
+    """This is not right."""
+    for var in some_random_list:
+        pass
+    print var
+
+
+def do_else(some_random_list):
+    """This is not right."""
+    for var in some_random_list:
+        if var == 42:
+            break
+    else:
+        var = 84
+    print var
+
diff --git a/test/messages/func_w0631.txt b/test/messages/func_w0631.txt
new file mode 100644
index 000000000..af335a178
--- /dev/null
+++ b/test/messages/func_w0631.txt
@@ -0,0 +1 @@
+W: 10:do_stuff: Using possibly undefined loop variable 'var'