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<title>6.21.3.5 Option attributes
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<H3><A NAME=
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6.21.3.5 Option attributes
The following option attributes may be passed as keyword arguments
to
<code>parser.add_option()
</code>. If you pass an option attribute
that is not relevant to a particular option, or fail to pass a required
option attribute,
<tt class=
"module">optparse
</tt> raises OptionError.
<tt class=
"member">action
</tt> (default:
<code>"store"</code>)
Determines
<tt class=
"module">optparse
</tt>'s behaviour when this option is seen on the command
line; the available options are documented above.
<tt class=
"member">type
</tt> (default:
<code>"string"</code>)
The argument type expected by this option (e.g.,
<code>"string"</code> or
<code>"int"</code>); the available option types are documented below.
<tt class=
"member">dest
</tt> (default: derived from option strings)
If the option's action implies writing or modifying a value somewhere,
this tells
<tt class=
"module">optparse
</tt> where to write it:
<tt class=
"member">dest
</tt> names an attribute of the
<code>options
</code> object that
<tt class=
"module">optparse
</tt> builds as it parses the command line.
<code>default
</code> (deprecated)
The value to use for this option's destination if the option is not
seen on the command line. Deprecated; use
<code>parser.set_defaults()
</code>
<code>nargs
</code> (default:
1)
How many arguments of type
<tt class=
"member">type
</tt> should be consumed when this
option is seen. If
> 1,
<tt class=
"module">optparse
</tt> will store a tuple of values to
<tt class=
"member">dest
</tt>.
For actions that store a constant value, the constant value to store.
For options of type
<code>"choice"</code>, the list of strings the user
For options with action
<code>"callback"</code>, the callable to call when this
option is seen. See section
<A href=
"optparse-option-callbacks.html#optparse-option-callbacks">6.21.4</A>, Option Callbacks for detail on the arguments
passed to
<code>callable
</code>.
<code>callback_args
</code>,
<code>callback_kwargs
</code>
Additional positional and keyword arguments to pass to
<code>callback
</code>
after the four standard callback arguments.
<tt class=
"member">help
</tt>
Help text to print for this option when listing all available options
after the user supplies a
<tt class=
"member">help
</tt> option (such as
<code>"-help"</code>).
If no help text is supplied, the option will be listed without help
text. To hide this option, use the special value
<code>SUPPRESS_HELP
</code>.
<code>metavar
</code> (default: derived from option strings)
Stand-in for the option argument(s) to use when printing help text.
See section
<A href=
"optparse-tutorial.html#optparse-tutorial">6.21.2</A>, the tutorial for an example.
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<span class=
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