.. currentmodule:: argparse
.. _upgrading-optparse-code:
==========================
Upgrading optparse code
==========================
Originally, the :mod:`argparse` module had attempted to maintain compatibility
with :mod:`optparse`. However, :mod:`optparse` was difficult to extend
transparently, particularly with the changes required to support
``nargs=`` specifiers and better usage messages. When most everything in
:mod:`optparse` had either been copy-pasted over or monkey-patched, it no
longer seemed practical to try to maintain the backwards compatibility.
The :mod:`argparse` module improves on the :mod:`optparse`
module in a number of ways including:
* Handling positional arguments.
* Supporting subcommands.
* Allowing alternative option prefixes like ``+`` and ``/``.
* Handling zero-or-more and one-or-more style arguments.
* Producing more informative usage messages.
* Providing a much simpler interface for custom ``type`` and ``action``.
A partial upgrade path from :mod:`optparse` to :mod:`argparse`:
* Replace all :meth:`optparse.OptionParser.add_option` calls with
:meth:`ArgumentParser.add_argument` calls.
* Replace ``(options, args) = parser.parse_args()`` with ``args =
parser.parse_args()`` and add additional :meth:`ArgumentParser.add_argument`
calls for the positional arguments. Keep in mind that what was previously
called ``options``, now in the :mod:`argparse` context is called ``args``.
* Replace :meth:`optparse.OptionParser.disable_interspersed_args`
by using :meth:`~ArgumentParser.parse_intermixed_args` instead of
:meth:`~ArgumentParser.parse_args`.
* Replace callback actions and the ``callback_*`` keyword arguments with
``type`` or ``action`` arguments.
* Replace string names for ``type`` keyword arguments with the corresponding
type objects (e.g. int, float, complex, etc).
* Replace :class:`optparse.Values` with :class:`Namespace` and
:exc:`optparse.OptionError` and :exc:`optparse.OptionValueError` with
:exc:`ArgumentError`.
* Replace strings with implicit arguments such as ``%default`` or ``%prog`` with
the standard Python syntax to use dictionaries to format strings, that is,
``%(default)s`` and ``%(prog)s``.
* Replace the OptionParser constructor ``version`` argument with a call to
``parser.add_argument('--version', action='version', version='<the version>')``.
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