Migrating optparse code to argparse¶
The argparse module offers several higher level features not natively
provided by the optparse 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 - typeand- action.
Originally, the argparse module attempted to maintain compatibility
with optparse.  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 parsing library, applications that are
currently using optparse 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 to argparse,
the following suggestions should be helpful:
- Replace all - optparse.OptionParser.add_option()calls with- ArgumentParser.add_argument()calls.
- Replace - (options, args) = parser.parse_args()with- args = parser.parse_args()and add additional- ArgumentParser.add_argument()calls for the positional arguments. Keep in mind that what was previously called- options, now in the- argparsecontext is called- args.
- Replace - optparse.OptionParser.disable_interspersed_args()by using- parse_intermixed_args()instead of- parse_args().
- Replace callback actions and the - callback_*keyword arguments with- typeor- actionarguments.
- Replace string names for - typekeyword arguments with the corresponding type objects (e.g. int, float, complex, etc).
- Replace - optparse.Valueswith- Namespaceand- optparse.OptionErrorand- optparse.OptionValueErrorwith- ArgumentError.
- Replace strings with implicit arguments such as - %defaultor- %progwith the standard Python syntax to use dictionaries to format strings, that is,- %(default)sand- %(prog)s.
- Replace the OptionParser constructor - versionargument with a call to- parser.add_argument('--version', action='version', version='<the version>').