From 1654d74e9a6250491bfb923424c4cf83af2af7a6 Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Tue, 25 Sep 2012 11:48:50 -0400
Subject: switch assertion to an explicit ValueError

---
 Lib/lib2to3/fixer_util.py | 4 ++--
 Lib/lib2to3/refactor.py   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Lib/lib2to3/fixer_util.py b/Lib/lib2to3/fixer_util.py
index 92f0da9..2b5bb1d 100644
--- a/Lib/lib2to3/fixer_util.py
+++ b/Lib/lib2to3/fixer_util.py
@@ -274,9 +274,9 @@ def find_root(node):
     """Find the top level namespace."""
     # Scamper up to the top level namespace
     while node.type != syms.file_input:
-        assert node.parent, "Tree is insane! root found before "\
-                           "file_input node was found."
         node = node.parent
+        if not node:
+            raise ValueError("root found before file_input node was found.")
     return node
 
 def does_tree_import(package, name, node):
diff --git a/Lib/lib2to3/refactor.py b/Lib/lib2to3/refactor.py
index 7cd034a..38fb8ed 100644
--- a/Lib/lib2to3/refactor.py
+++ b/Lib/lib2to3/refactor.py
@@ -445,7 +445,7 @@ class RefactoringTool(object):
 
                         try:
                             find_root(node)
-                        except AssertionError:
+                        except ValueError:
                             # this node has been cut off from a
                             # previous transformation ; skip
                             continue
-- 
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