- version-neutral syntax for print and exec
- version-neutral exception handling: use exc_info()
- version-neutral exception raising: use raise A("x"), not A, "x"
- use e.args[0] instead of e[0]
- use urllib.request if urllib2 unavailable
- use http.client if httplib not available
- use socketserver if SocketServer not available
- use test.support if test_support not available