diff --git a/Lib/dumbdbm.py b/Lib/dumbdbm.py
index 7724ac6..eb1c613 100644
--- a/Lib/dumbdbm.py
+++ b/Lib/dumbdbm.py
@@ -21,12 +21,11 @@
 
 """
 
+import io as _io
 import os as _os
 import __builtin__
 import UserDict
 
-_open = __builtin__.open
-
 _BLOCKSIZE = 512
 
 error = IOError                         # For anydbm
@@ -42,7 +41,7 @@
     # _commit() finish successfully, we can't ignore shutdown races
     # here, and _commit() must not reference any globals.
     _os = _os       # for _commit()
-    _open = _open   # for _commit()
+    _io = _io       # for _commit()
 
     def __init__(self, filebasename, mode):
         self._mode = mode
@@ -66,9 +65,9 @@
 
         # Mod by Jack: create data file if needed
         try:
-            f = _open(self._datfile, 'r')
+            f = _io.open(self._datfile, 'r')
         except IOError:
-            f = _open(self._datfile, 'w')
+            f = _io.open(self._datfile, 'w')
             self._chmod(self._datfile)
         f.close()
         self._update()
@@ -77,7 +76,7 @@
     def _update(self):
         self._index = {}
         try:
-            f = _open(self._dirfile)
+            f = _io.open(self._dirfile, 'r')
         except IOError:
             pass
         else:
@@ -107,7 +106,7 @@
         except self._os.error:
             pass
 
-        f = self._open(self._dirfile, 'w')
+        f = self._io.open(self._dirfile, 'w')
         self._chmod(self._dirfile)
         for key, pos_and_siz_pair in self._index.items():
             f.write("%r, %r\n" % (key, pos_and_siz_pair))
@@ -117,7 +116,7 @@
 
     def __getitem__(self, key):
         pos, siz = self._index[key]     # may raise KeyError
-        f = _open(self._datfile, 'rb')
+        f = _io.open(self._datfile, 'rb')
         f.seek(pos)
         dat = f.read(siz)
         f.close()
@@ -128,11 +127,11 @@
     # to get to an aligned offset.  Return pair
     #     (starting offset of val, len(val))
     def _addval(self, val):
-        f = _open(self._datfile, 'rb+')
+        f = _io.open(self._datfile, 'rb+')
         f.seek(0, 2)
         pos = int(f.tell())
         npos = ((pos + _BLOCKSIZE - 1) // _BLOCKSIZE) * _BLOCKSIZE
-        f.write('\0'*(npos-pos))
+        f.write(b'\0'*(npos-pos))
         pos = npos
         f.write(val)
         f.close()
@@ -143,7 +142,7 @@
     # pos to hold val, without overwriting some other value.  Return
     # pair (pos, len(val)).
     def _setval(self, pos, val):
-        f = _open(self._datfile, 'rb+')
+        f = _io.open(self._datfile, 'rb+')
         f.seek(pos)
         f.write(val)
         f.close()
@@ -154,14 +153,16 @@
     # the in-memory index dict, and append one to the directory file.
     def _addkey(self, key, pos_and_siz_pair):
         self._index[key] = pos_and_siz_pair
-        f = _open(self._dirfile, 'a')
+        f = _io.open(self._dirfile, 'a')
         self._chmod(self._dirfile)
         f.write("%r, %r\n" % (key, pos_and_siz_pair))
         f.close()
 
     def __setitem__(self, key, val):
-        if not type(key) == type('') == type(val):
-            raise TypeError, "keys and values must be strings"
+        if not isinstance(key, basestring):
+            raise TypeError("keys must be strings")
+        if not isinstance(val, (str8, bytes)):
+            raise TypeError("values must be byte strings")
         if key not in self._index:
             self._addkey(key, self._addval(val))
         else:
diff --git a/Lib/test/test_anydbm.py b/Lib/test/test_anydbm.py
index f980354..f5eae42 100644
--- a/Lib/test/test_anydbm.py
+++ b/Lib/test/test_anydbm.py
@@ -21,13 +21,13 @@
             pass
 
 class AnyDBMTestCase(unittest.TestCase):
-    _dict = {'0': '',
-             'a': 'Python:',
-             'b': 'Programming',
-             'c': 'the',
-             'd': 'way',
-             'f': 'Guido',
-             'g': 'intended'
+    _dict = {'0': b'',
+             'a': b'Python:',
+             'b': b'Programming',
+             'c': b'the',
+             'd': b'way',
+             'f': b'Guido',
+             'g': b'intended',
              }
 
     def __init__(self, *args):
@@ -44,7 +44,7 @@
     def test_anydbm_modification(self):
         self.init_db()
         f = anydbm.open(_fname, 'c')
-        self._dict['g'] = f['g'] = "indented"
+        self._dict['g'] = f['g'] = b"indented"
         self.read_helper(f)
         f.close()
 
diff --git a/Lib/test/test_dumbdbm.py b/Lib/test/test_dumbdbm.py
index ba94d98..c7d29ec 100644
--- a/Lib/test/test_dumbdbm.py
+++ b/Lib/test/test_dumbdbm.py
@@ -3,6 +3,7 @@
    Original by Roger E. Masse
 """
 
+import io
 import os
 import unittest
 import dumbdbm
@@ -18,13 +19,13 @@
             pass
 
 class DumbDBMTestCase(unittest.TestCase):
-    _dict = {'0': '',
-             'a': 'Python:',
-             'b': 'Programming',
-             'c': 'the',
-             'd': 'way',
-             'f': 'Guido',
-             'g': 'intended'
+    _dict = {'0': b'',
+             'a': b'Python:',
+             'b': b'Programming',
+             'c': b'the',
+             'd': b'way',
+             'f': b'Guido',
+             'g': b'intended',
              }
 
     def __init__(self, *args):
@@ -64,15 +65,15 @@
 
     def test_close_twice(self):
         f = dumbdbm.open(_fname)
-        f['a'] = 'b'
-        self.assertEqual(f['a'], 'b')
+        f['a'] = b'b'
+        self.assertEqual(f['a'], b'b')
         f.close()
         f.close()
 
     def test_dumbdbm_modification(self):
         self.init_db()
         f = dumbdbm.open(_fname, 'w')
-        self._dict['g'] = f['g'] = "indented"
+        self._dict['g'] = f['g'] = b"indented"
         self.read_helper(f)
         f.close()
 
@@ -91,29 +92,29 @@
     def test_write_write_read(self):
         # test for bug #482460
         f = dumbdbm.open(_fname)
-        f['1'] = 'hello'
-        f['1'] = 'hello2'
+        f['1'] = b'hello'
+        f['1'] = b'hello2'
         f.close()
         f = dumbdbm.open(_fname)
-        self.assertEqual(f['1'], 'hello2')
+        self.assertEqual(f['1'], b'hello2')
         f.close()
 
     def test_line_endings(self):
         # test for bug #1172763: dumbdbm would die if the line endings
         # weren't what was expected.
         f = dumbdbm.open(_fname)
-        f['1'] = 'hello'
-        f['2'] = 'hello2'
+        f['1'] = b'hello'
+        f['2'] = b'hello2'
         f.close()
 
         # Mangle the file by adding \r before each newline
-        data = open(_fname + '.dir').read()
-        data = data.replace('\n', '\r\n')
-        open(_fname + '.dir', 'wb').write(data)
+        data = io.open(_fname + '.dir', 'rb').read()
+        data = data.replace(b'\n', b'\r\n')
+        io.open(_fname + '.dir', 'wb').write(data)
 
         f = dumbdbm.open(_fname)
-        self.assertEqual(f['1'], 'hello')
-        self.assertEqual(f['2'], 'hello2')
+        self.assertEqual(f['1'], b'hello')
+        self.assertEqual(f['2'], b'hello2')
 
 
     def read_helper(self, f):
@@ -147,7 +148,7 @@
                         del d[k]
                         del f[k]
                 else:
-                    v = random.choice('abc') * random.randrange(10000)
+                    v = random.choice((b'a', b'b', b'c')) * random.randrange(10000)
                     d[k] = v
                     f[k] = v
                     self.assertEqual(f[k], v)
diff --git a/Lib/test/test_gdbm.py b/Lib/test/test_gdbm.py
index ae76e39..4daca61 100755
--- a/Lib/test/test_gdbm.py
+++ b/Lib/test/test_gdbm.py
@@ -12,7 +12,7 @@
 g = gdbm.open(filename, 'c')
 verify(g.keys() == [])
 g['a'] = 'b'
-g['12345678910'] = '019237410982340912840198242'
+g['12345678910'] = b'019237410982340912840198242'
 a = g.keys()
 if verbose:
     print('Test gdbm file keys: ', a)
diff --git a/Lib/test/test_whichdb.py b/Lib/test/test_whichdb.py
index f2652c1..6cb5e4f 100644
--- a/Lib/test/test_whichdb.py
+++ b/Lib/test/test_whichdb.py
@@ -51,7 +51,7 @@
         self.assertEqual(name, whichdb.whichdb(_fname))
         # Now add a key
         f = mod.open(_fname, 'w')
-        f["1"] = "1"
+        f["1"] = b"1"
         f.close()
         self.assertEqual(name, whichdb.whichdb(_fname))
     setattr(WhichDBTestCase,"test_whichdb_%s" % name, test_whichdb_name)
diff --git a/Lib/whichdb.py b/Lib/whichdb.py
index 4d7a560..752bbb1 100644
--- a/Lib/whichdb.py
+++ b/Lib/whichdb.py
@@ -1,6 +1,7 @@
 # !/usr/bin/env python
 """Guess which db package to use to open a db file."""
 
+import io
 import os
 import struct
 import sys
@@ -29,18 +30,18 @@
 
     # Check for dbm first -- this has a .pag and a .dir file
     try:
-        f = open(filename + os.extsep + "pag", "rb")
+        f = io.open(filename + os.extsep + "pag", "rb")
         f.close()
         # dbm linked with gdbm on OS/2 doesn't have .dir file
         if not (dbm.library == "GNU gdbm" and sys.platform == "os2emx"):
-            f = open(filename + os.extsep + "dir", "rb")
+            f = io.open(filename + os.extsep + "dir", "rb")
             f.close()
         return "dbm"
     except IOError:
         # some dbm emulations based on Berkeley DB generate a .db file
         # some do not, but they should be caught by the dbhash checks
         try:
-            f = open(filename + os.extsep + "db", "rb")
+            f = io.open(filename + os.extsep + "db", "rb")
             f.close()
             # guarantee we can actually open the file using dbm
             # kind of overkill, but since we are dealing with emulations
@@ -60,9 +61,9 @@
         # dumbdbm files with no keys are empty
         if size == 0:
             return "dumbdbm"
-        f = open(filename + os.extsep + "dir", "rb")
+        f = io.open(filename + os.extsep + "dir", "rb")
         try:
-            if f.read(1) in ("'", '"'):
+            if f.read(1) in (b"'", b'"'):
                 return "dumbdbm"
         finally:
             f.close()
@@ -71,7 +72,7 @@
 
     # See if the file exists, return None if not
     try:
-        f = open(filename, "rb")
+        f = io.open(filename, "rb")
     except IOError:
         return None