Whack dem moles.

src/ZODB/_compat.py

@@ -80,3 +80,13 @@ except NameError:
     # Py3
     long = int
 
+
+try:
+    TEXT = unicode
+except NameError: #pragma NO COVER Py3k
+    TEXT = str
+
+def ascii_bytes(x):
+    if isinstance(x, TEXT):
+        x = x.encode('ascii')
+    return x

src/ZODB/blob.py

@@ -31,7 +31,10 @@ import ZODB.interfaces
 from ZODB.interfaces import BlobError
 from ZODB import utils
 from ZODB.POSException import POSKeyError
-from ZODB._compat import BytesIO, Unpickler, decodebytes
+from ZODB._compat import BytesIO
+from ZODB._compat import Unpickler
+from ZODB._compat import decodebytes
+from ZODB._compat import ascii_bytes
 
 
 if sys.version_info[0] >= 3:
@@ -557,7 +560,7 @@ class BushyLayout(object):
     def path_to_oid(self, path):
         if self.blob_path_pattern.match(path) is None:
             raise ValueError("Not a valid OID path: `%s`" % path)
-        path = [bytes(x, 'ascii') for x in path.split(os.path.sep)]
+        path = [ascii_bytes(x) for x in path.split(os.path.sep)]
         # Each path segment stores a byte in hex representation. Turn it into
         # an int and then get the character for our byte string.
         oid = b''.join(binascii.unhexlify(byte[2:]) for byte in path)

src/ZODB/utils.py

@@ -22,7 +22,9 @@ from tempfile import mkstemp
 
 from persistent.TimeStamp import TimeStamp
 
-from ZODB._compat import Unpickler, BytesIO
+from ZODB._compat import Unpickler
+from ZODB._compat import BytesIO
+from ZODB._compat import ascii_bytes
 
 
 __all__ = ['z64',
@@ -164,8 +166,7 @@ def oid_repr(oid):
         return repr(oid)
 
 def repr_to_oid(repr):
-    if not isinstance(repr, bytes):
-        repr = bytes(repr, 'ascii')
+    repr = ascii_bytes(repr)
     if repr.startswith(b"0x"):
         repr = repr[2:]
     as_bin = unhexlify(repr)