According to Jeffrey Honig, bsd/os 4.0 should be added to the list.

Lib/test/test_fcntl.py

@@ -16,7 +16,9 @@ rv = fcntl.fcntl(f.fileno(), FCNTL.F_SETFL, os.O_NONBLOCK)
 if verbose:
     print 'Status from fnctl with O_NONBLOCK: ', rv
     
-if sys.platform in ('netbsd1', 'freebsd2', 'freebsd3', 'bsdos2', 'bsdos3'):
+if sys.platform in ('netbsd1',
+                    'freebsd2', 'freebsd3',
+                    'bsdos2', 'bsdos3', 'bsdos4'):
     lockdata = struct.pack('lxxxxlxxxxlhh', 0, 0, 0, FCNTL.F_WRLCK, 0)
 elif sys.platform in ['aix3', 'aix4']:
     lockdata = struct.pack('hhlllii', FCNTL.F_WRLCK, 0, 0, 0, 0, 0, 0)