https://github.com/python/cpython/commit/32bc8e83db3bcca7138dbd23e7925c0a5217c0a0 commit: 32bc8e83db3bcca7138dbd23e7925c0a5217c0a0 branch: 3.12 author: Miss Islington (bot) <[email protected]> committer: serhiy-storchaka <[email protected]> date: 2024-11-22T14:13:43Z summary:
[3.12] GH-122679: Add `register()` to argparse docs (GH-126939) (GH-127148) (cherry picked from commit fcfdb55465636afc256bc29781b283404d88e6ca) Co-authored-by: Savannah Ostrowski <[email protected]> files: M Doc/library/argparse.rst diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst index b142135f6e635b..00d7c384946cf1 100644 --- a/Doc/library/argparse.rst +++ b/Doc/library/argparse.rst @@ -750,7 +750,8 @@ Only actions that consume command-line arguments (e.g. ``'store'``, The recommended way to create a custom action is to extend :class:`Action`, overriding the :meth:`!__call__` method and optionally the :meth:`!__init__` and -:meth:`!format_usage` methods. +:meth:`!format_usage` methods. You can also register custom actions using the +:meth:`~ArgumentParser.register` method and reference them by their registered name. An example of a custom action:: @@ -971,10 +972,11 @@ necessary type-checking and type conversions to be performed. If the type_ keyword is used with the default_ keyword, the type converter is only applied if the default is a string. -The argument to ``type`` can be any callable that accepts a single string. +The argument to ``type`` can be a callable that accepts a single string or +the name of a registered type (see :meth:`~ArgumentParser.register`) If the function raises :exc:`ArgumentTypeError`, :exc:`TypeError`, or :exc:`ValueError`, the exception is caught and a nicely formatted error -message is displayed. No other exception types are handled. +message is displayed. Other exception types are not handled. Common built-in types and functions can be used as type converters: @@ -2058,6 +2060,34 @@ Intermixed parsing .. versionadded:: 3.7 +Registering custom types or actions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +.. method:: ArgumentParser.register(registry_name, value, object) + + Sometimes it's desirable to use a custom string in error messages to provide + more user-friendly output. In these cases, :meth:`!register` can be used to + register custom actions or types with a parser and allow you to reference the + type by their registered name instead of their callable name. + + The :meth:`!register` method accepts three arguments - a *registry_name*, + specifying the internal registry where the object will be stored (e.g., + ``action``, ``type``), *value*, which is the key under which the object will + be registered, and object, the callable to be registered. + + The following example shows how to register a custom type with a parser:: + + >>> import argparse + >>> parser = argparse.ArgumentParser() + >>> parser.register('type', 'hexadecimal integer', lambda s: int(s, 16)) + >>> parser.add_argument('--foo', type='hexadecimal integer') + _StoreAction(option_strings=['--foo'], dest='foo', nargs=None, const=None, default=None, type='hexadecimal integer', choices=None, required=False, help=None, metavar=None, deprecated=False) + >>> parser.parse_args(['--foo', '0xFA']) + Namespace(foo=250) + >>> parser.parse_args(['--foo', '1.2']) + usage: PROG [-h] [--foo FOO] + PROG: error: argument --foo: invalid 'hexadecimal integer' value: '1.2' + Exceptions ---------- _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-checkins.python.org/ Member address: [email protected]
