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14.3.3.5 Option attributes

The following option attributes may be passed as keyword arguments to `parser.add_option()`. If you pass an option attribute that is not relevant to a particular option, or fail to pass a required option attribute, `optparse` raises OptionError.

- `action` (default: `"store"`)

  Determines `optparse`'s behaviour when this option is seen on the command line; the available options are documented above.

- `type` (default: `"string"`)

  The argument type expected by this option (e.g., `"string"` or `"int"`); the available option types are documented below.

- `dest` (default: derived from option strings)

  If the option's action implies writing or modifying a value somewhere, this tells `optparse` where to write it: `dest` names an attribute of the `options` object that `optparse` builds as it parses the command line.

- `default` (deprecated)

  The value to use for this option's destination if the option is not seen on the command line. Deprecated; use `parser.set_defaults()` instead.

- `nargs` (default: 1)

  How many arguments of type `type` should be consumed when this option is seen. If > 1, `optparse` will store a tuple of values to `dest`.

- `const`

  For actions that store a constant value, the constant value to store.

- `choices`

  For options of type `"choice"`, the list of strings the user may choose from.

- `callback`

  For options with action `"callback"`, the callable to call when this option is seen. See section 14.3.4, Option Callbacks for detail on the arguments passed to `callable`.

- `callback_args`, `callback_kwargs`

  Additional positional and keyword arguments to pass to `callback` after the four standard callback arguments.

- `help`

  Help text to print for this option when listing all available options after the user supplies a `help` option (such as --help). If no help text is supplied, the option will be listed without help text. To hide this option, use the special value `SUPPRESS_HELP`.

- `metavar` (default: derived from option strings)

  Stand-in for the option argument(s) to use when printing help text. See section 14.3.2, the tutorial for an example.