Index: Lib/base64.py
===================================================================
--- Lib/base64.py	(revision 71822)
+++ Lib/base64.py	(working copy)
@@ -329,28 +329,31 @@
         output.write(s)
 
 
-def encodestring(s):
-    """Encode a string into multiple lines of base-64 data.
+def encodebytes(s):
+    """Encode bytes into multiple lines of base-64 data.
 
-    Argument and return value are bytes.
+    Argument type is bytes, return type is str.
     """
     if not isinstance(s, bytes_types):
         raise TypeError("expected bytes, not %s" % s.__class__.__name__)
     pieces = []
     for i in range(0, len(s), MAXBINSIZE):
         chunk = s[i : i + MAXBINSIZE]
-        pieces.append(binascii.b2a_base64(chunk))
-    return b"".join(pieces)
+        pieces.append(binascii.b2a_base64(chunk).decode("ascii"))
+    return "".join(pieces)
 
+# For historical reasons
+encodestring = encodebytes
 
+
 def decodestring(s):
     """Decode a string.
 
-    Argument and return value are bytes.
+    Argument type is str, return type is bytes.
     """
-    if not isinstance(s, bytes_types):
-        raise TypeError("expected bytes, not %s" % s.__class__.__name__)
-    return binascii.a2b_base64(s)
+    if not isinstance(s, str):
+        raise TypeError("expected str, not %s" % s.__class__.__name__)
+    return binascii.a2b_base64(s.encode("ascii"))
 
 
 
Index: Lib/test/test_base64.py
===================================================================
--- Lib/test/test_base64.py	(revision 71822)
+++ Lib/test/test_base64.py	(working copy)
@@ -6,35 +6,36 @@
 
 
 class LegacyBase64TestCase(unittest.TestCase):
-    def test_encodestring(self):
+    def test_encodebytes(self):
         eq = self.assertEqual
-        eq(base64.encodestring(b"www.python.org"), b"d3d3LnB5dGhvbi5vcmc=\n")
-        eq(base64.encodestring(b"a"), b"YQ==\n")
-        eq(base64.encodestring(b"ab"), b"YWI=\n")
-        eq(base64.encodestring(b"abc"), b"YWJj\n")
-        eq(base64.encodestring(b""), b"")
-        eq(base64.encodestring(b"abcdefghijklmnopqrstuvwxyz"
+        eq(base64.encodebytes(b"www.python.org"), "d3d3LnB5dGhvbi5vcmc=\n")
+        eq(base64.encodebytes(b"a"), "YQ==\n")
+        eq(base64.encodebytes(b"ab"), "YWI=\n")
+        eq(base64.encodebytes(b"abc"), "YWJj\n")
+        eq(base64.encodebytes(b""), "")
+        eq(base64.encodebytes(b"abcdefghijklmnopqrstuvwxyz"
                                b"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                b"0123456789!@#0^&*();:<>,. []{}"),
-           b"YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
-           b"RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT"
-           b"Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n")
-        self.assertRaises(TypeError, base64.encodestring, "")
+           "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
+           "RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT"
+           "Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n")
+        self.assertRaises(TypeError, base64.encodebytes, "")
+        eq(base64.encodestring(b"www.python.org"), "d3d3LnB5dGhvbi5vcmc=\n")
 
     def test_decodestring(self):
         eq = self.assertEqual
-        eq(base64.decodestring(b"d3d3LnB5dGhvbi5vcmc=\n"), b"www.python.org")
-        eq(base64.decodestring(b"YQ==\n"), b"a")
-        eq(base64.decodestring(b"YWI=\n"), b"ab")
-        eq(base64.decodestring(b"YWJj\n"), b"abc")
-        eq(base64.decodestring(b"YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
-                               b"RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT"
-                               b"Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n"),
+        eq(base64.decodestring("d3d3LnB5dGhvbi5vcmc=\n"), b"www.python.org")
+        eq(base64.decodestring("YQ==\n"), b"a")
+        eq(base64.decodestring("YWI=\n"), b"ab")
+        eq(base64.decodestring("YWJj\n"), b"abc")
+        eq(base64.decodestring("YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
+                               "RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT"
+                               "Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n"),
            b"abcdefghijklmnopqrstuvwxyz"
            b"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            b"0123456789!@#0^&*();:<>,. []{}")
-        eq(base64.decodestring(b''), b'')
-        self.assertRaises(TypeError, base64.decodestring, "")
+        eq(base64.decodestring(''), b'')
+        self.assertRaises(TypeError, base64.decodestring, b"")
 
     def test_encode(self):
         eq = self.assertEqual