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<title>6.21.4 Option Callbacks
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<H2><A NAME=
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"optparse-option-callbacks"></A>
When
<tt class=
"module">optparse
</tt>'s built-in actions and types aren't quite enough for your
needs, you have two choices: extend
<tt class=
"module">optparse
</tt> or define a callback option.
Extending
<tt class=
"module">optparse
</tt> is more general, but overkill for a lot of simple
cases. Quite often a simple callback is all you need.
There are two steps to defining a callback option:
define the option itself using the
<code>callback
</code> action
write the callback; this is a function (or method) that
takes at least four arguments, as described below
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<A NAME=
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<LI><A href=
"optparse-defining-callback-option.html">6.21.4.1 Defining a callback option
</a>
<LI><A href=
"optparse-how-callbacks-called.html">6.21.4.2 How callbacks are called
</a>
<LI><A href=
"optparse-raising-errors-in-callback.html">6.21.4.3 Raising errors in a callback
</a>
<LI><A href=
"optparse-callback-example-1.html">6.21.4.4 Callback example
1: trivial callback
</a>
<LI><A href=
"optparse-callback-example-2.html">6.21.4.5 Callback example
2: check option order
</a>
<LI><A href=
"optparse-callback-example-3.html">6.21.4.6 Callback example
3: check option order (generalized)
</a>
<LI><A href=
"optparse-callback-example-4.html">6.21.4.7 Callback example
4: check arbitrary condition
</a>
<LI><A href=
"optparse-callback-example-5.html">6.21.4.8 Callback example
5: fixed arguments
</a>
<LI><A href=
"optparse-callback-example-6.html">6.21.4.9 Callback example
6: variable arguments
</a>
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<span class=
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2.4.2, documentation updated on
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2005.
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