--- a/Lib/gzip.py	Mon Jun 18 15:54:57 2012 +0100
+++ b/Lib/gzip.py	Wed Jun 20 01:35:22 2012 +0200
@@ -159,9 +159,8 @@
         if fileobj is None:
             fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
         if filename is None:
-            if hasattr(fileobj, 'name') and isinstance(fileobj.name, str):
-                filename = fileobj.name
-            else:
+            filename = getattr(fileobj, 'name', '')
+            if not isinstance(filename, (str, bytes)):
                 filename = ''
         if mode is None:
             if hasattr(fileobj, 'mode'): mode = fileobj.mode
@@ -236,7 +235,8 @@
             # RFC 1952 requires the FNAME field to be Latin-1. Do not
             # include filenames that cannot be represented that way.
             fname = os.path.basename(self.name)
-            fname = fname.encode('latin-1')
+            if not isinstance(fname, bytes):
+                fname = fname.encode('latin-1')
             if fname.endswith(b'.gz'):
                 fname = fname[:-3]
         except UnicodeEncodeError: