No compatibility layer. Its really not bad.

there are a few modules that are simply at different locations but have the same API

  if PY3:
    from http import client as httplib
  else:
    import httplib

constants

  PY3 = sys.version_info >= (3, 0)
  PY2 = sys.version_info < (3, 0)
  
  PY26 = sys.version_info >= (2, 6) and sys.version_info < (2, 7)

is string

  isinstance(<maybe_string>, basestring if PY2 else str)

using different classes

  # Python 2.6 doesn't properly UTF-8 encode syslog messages, so it needs
  # to be performed in a custom formatter.
  formatter_class = UnicodeLoggingFormatter if PY26 else logging.Formatter