Index: Lib/urllib/parse.py
===================================================================
--- Lib/urllib/parse.py	(revision 64756)
+++ Lib/urllib/parse.py	(working copy)
@@ -259,21 +259,24 @@
         return url, ''
 
 
-_hextochr = dict(('%02x' % i, chr(i)) for i in range(256))
-_hextochr.update(('%02X' % i, chr(i)) for i in range(256))
+_hextochr = dict((('%02x' % i).encode('ascii'), bytes([i]))
+                    for i in range(256))
+_hextochr.update((('%02X' % i).encode('ascii'), bytes([i]))
+                    for i in range(256))
 
 def unquote(s):
     """unquote('abc%20def') -> 'abc def'."""
-    res = s.split('%')
+    # Manipulate as bytes rather than str, so we can
+    # decode from UTF-8 at the end.
+    res = s.encode("utf-8").split(b'%')
     for i in range(1, len(res)):
         item = res[i]
         try:
             res[i] = _hextochr[item[:2]] + item[2:]
         except KeyError:
-            res[i] = '%' + item
-        except UnicodeDecodeError:
-            res[i] = chr(int(item[:2], 16)) + item[2:]
-    return "".join(res)
+            res[i] = b'%' + item
+    # Replace malformed UTF-8 sequences with '\ufffd'
+    return b"".join(res).decode("utf-8", "replace")
 
 def unquote_plus(s):
     """unquote('%7e/abc+def') -> '~/abc def'"""
@@ -294,12 +297,17 @@
         try:
             return self.cache[c]
         except KeyError:
-            if ord(c) < 256:
+            if ord(c) < 128:
                 res = (c in self.safe) and c or ('%%%02X' % ord(c))
                 self.cache[c] = res
                 return res
             else:
-                return "".join(['%%%02X' % i for i in c.encode("utf-8")])
+                if c in self.safe:
+                    res = c
+                else:
+                    res = "".join(['%%%02X' % i for i in c.encode("utf-8")])
+                self.cache[c] = res
+                return res
 
 def quote(s, safe = '/'):
     """quote('abc def') -> 'abc%20def'
Index: Lib/test/test_urllib.py
===================================================================
--- Lib/test/test_urllib.py	(revision 64756)
+++ Lib/test/test_urllib.py	(working copy)
@@ -465,7 +465,7 @@
 
     def test_unquote_with_unicode(self):
         r = urllib.parse.unquote('br%C3%BCckner_sapporo_20050930.doc')
-        self.assertEqual(r, 'br\xc3\xbcckner_sapporo_20050930.doc')
+        self.assertEqual(r, 'br\u00fcckner_sapporo_20050930.doc')
 
 class urlencode_Tests(unittest.TestCase):
     """Tests for urlencode()"""