python_doc_md/Beginner/howto/argparse-optparse.md

::: currentmodule argparse :::

Migrating optparse code to argparse[]{#upgrading-optparse-code} {#migrating-optparse-code}

The argparse{.interpreted-text role="mod"} module offers several higher level features not natively provided by the optparse{.interpreted-text role="mod"} module, 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.

Originally, the argparse{.interpreted-text role="mod"} module attempted to maintain compatibility with optparse{.interpreted-text role="mod"}. However, the fundamental design differences between supporting declarative command line option processing (while leaving positional argument processing to application code), and supporting both named options and positional arguments in the declarative interface mean that the API has diverged from that of optparse over time.

As described in choosing-an-argument-parser{.interpreted-text role="ref"}, applications that are currently using optparse{.interpreted-text role="mod"} and are happy with the way it works can just continue to use optparse.

Application developers that are considering migrating should also review the list of intrinsic behavioural differences described in that section before deciding whether or not migration is desirable.

For applications that do choose to migrate from optparse{.interpreted-text role="mod"} to argparse{.interpreted-text role="mod"}, the following suggestions should be helpful:

• Replace all optparse.OptionParser.add_option{.interpreted-text role="meth"} calls with ArgumentParser.add_argument{.interpreted-text role="meth"} calls.
• Replace (options, args) = parser.parse_args() with args = parser.parse_args() and add additional ArgumentParser.add_argument{.interpreted-text role="meth"} calls for the positional arguments. Keep in mind that what was previously called options, now in the argparse{.interpreted-text role="mod"} context is called args.
• Replace optparse.OptionParser.disable_interspersed_args{.interpreted-text role="meth"} by using ~ArgumentParser.parse_intermixed_args{.interpreted-text role="meth"} instead of ~ArgumentParser.parse_args{.interpreted-text role="meth"}.
• 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 optparse.Values{.interpreted-text role="class"} with Namespace{.interpreted-text role="class"} and optparse.OptionError{.interpreted-text role="exc"} and optparse.OptionValueError{.interpreted-text role="exc"} with ArgumentError{.interpreted-text role="exc"}.
• 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>').