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diff --git a/lib/python2.7/lib2to3/pgen2/literals.py b/lib/python2.7/lib2to3/pgen2/literals.py
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+++ b/lib/python2.7/lib2to3/pgen2/literals.py
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+# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+"""Safely evaluate Python string literals without using eval()."""
+
+import re
+
+simple_escapes = {"a": "\a",
+                  "b": "\b",
+                  "f": "\f",
+                  "n": "\n",
+                  "r": "\r",
+                  "t": "\t",
+                  "v": "\v",
+                  "'": "'",
+                  '"': '"',
+                  "\\": "\\"}
+
+def escape(m):
+    all, tail = m.group(0, 1)
+    assert all.startswith("\\")
+    esc = simple_escapes.get(tail)
+    if esc is not None:
+        return esc
+    if tail.startswith("x"):
+        hexes = tail[1:]
+        if len(hexes) < 2:
+            raise ValueError("invalid hex string escape ('\\%s')" % tail)
+        try:
+            i = int(hexes, 16)
+        except ValueError:
+            raise ValueError("invalid hex string escape ('\\%s')" % tail)
+    else:
+        try:
+            i = int(tail, 8)
+        except ValueError:
+            raise ValueError("invalid octal string escape ('\\%s')" % tail)
+    return chr(i)
+
+def evalString(s):
+    assert s.startswith("'") or s.startswith('"'), repr(s[:1])
+    q = s[0]
+    if s[:3] == q*3:
+        q = q*3
+    assert s.endswith(q), repr(s[-len(q):])
+    assert len(s) >= 2*len(q)
+    s = s[len(q):-len(q)]
+    return re.sub(r"\\(\'|\"|\\|[abfnrtv]|x.{0,2}|[0-7]{1,3})", escape, s)
+
+def test():
+    for i in range(256):
+        c = chr(i)
+        s = repr(c)
+        e = evalString(s)
+        if e != c:
+            print i, c, s, e
+
+
+if __name__ == "__main__":
+    test()