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

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

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

  # 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

As the maintainer of WebOb/Pyramid/Waitress we have a compat module that contains all of the changes/renames/functions to help with the Python2/3 compatibility and all tests run across both platforms.

Are the functions borrowed heavily from six? Yes, but we don't need to vendor all of six.