2to3

This document describes user-visible changes from pykickstart-2 to
pykickstart-3.  With the major version number change, I've taken the
opportunity to make some changes that would break compatibility.  In order
to use the new version, these are things you should be aware of:

* KickstartValueError is no longer raised in pykickstart.  Any places that
  would have raised this exception now raise KickstartParseError.  The old
  KickstartValueError class still exists, should you have code that needs
  to raise it.

* The map and map_extend actions provided by KSOptionParser have been
  eliminated.  Nothing in pykickstart outside of the firewall command used
  these actions, and it's easy enough to implement without custom actions.

* The KSOption class has been removed.

* _setToSelf has been renamed set_to_self to reflect that it's really a public
  function, and now only takes an argparse.Namespace argument.  _setToObj has
  similarly been renamed set_to_obj, and now only takes a source
  argparse.Namespace and a destination object.  The old names still exist as
  wrappers for the new names.

* pykickstart now uses the argparse module instead of the deprecated optparse
  module.  The bulk of the changes for this release are related to this move.
  If you have your own commands or have subclassed existing commands, you
  will need to make a variety of changes to your code.  The rest of the items
  in this list are due to this change.

  In general, see:

  https://docs.python.org/3/library/argparse.html#upgrading-optparse-code

* add_option is now add_argument.

* parse_args now returns only one value, an argparse.Namespace instance.  It
  is recommended you use parse_args for commands that don't expect any extra
  arguments and parse_known_args for any commands that do.  parse_known_args
  returns both an argparse.Namespace and a list of extra options.  Examples
  of commands that should use parse_known_args are things like logvol or part,
  that want a mount point.

* The callback action no longer exists.  If you need to do some complex
  conversion of the value given as the argument, use type=<some function> to do
  it.  See the autopart command for an example.  If you need to set multiple
  values when one argument is seen, you'll need to set an intermediate value
  and do the real setting in the parse method.  See the bootloader command.

* There is no need to specify type="choice" any more.  Just give choices=.

* There are new ExtendAction and ExtendConstActions available.  The first
  extends an existing list with a list of new values.  This is useful if an
  argument can be provided multiple times and each time can take a comma
  separated list of values.  The second does the same, but with a given
  const= value.  See the firewall command for an example.