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| <title>Debugging with GDB: Functions In Python</title> |
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| Next: <a href="Progspaces-In-Python.html#Progspaces-In-Python" accesskey="n" rel="next">Progspaces In Python</a>, Previous: <a href="Parameters-In-Python.html#Parameters-In-Python" accesskey="p" rel="prev">Parameters In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Writing-new-convenience-functions"></a> |
| <h4 class="subsubsection">23.2.2.21 Writing new convenience functions</h4> |
| |
| <a name="index-writing-convenience-functions"></a> |
| <a name="index-convenience-functions-in-python"></a> |
| <a name="index-python-convenience-functions"></a> |
| <a name="index-gdb_002eFunction"></a> |
| <a name="index-Function"></a> |
| <p>You can implement new convenience functions (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>) |
| in Python. A convenience function is an instance of a subclass of the |
| class <code>gdb.Function</code>. |
| </p> |
| <dl> |
| <dt><a name="index-Function_002e_005f_005finit_005f_005f"></a>Function: <strong>Function.__init__</strong> <em>(name)</em></dt> |
| <dd><p>The initializer for <code>Function</code> registers the new function with |
| <small>GDB</small>. The argument <var>name</var> is the name of the function, |
| a string. The function will be visible to the user as a convenience |
| variable of type <code>internal function</code>, whose name is the same as |
| the given <var>name</var>. |
| </p> |
| <p>The documentation for the new function is taken from the documentation |
| string for the new class. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Function_002einvoke"></a>Function: <strong>Function.invoke</strong> <em>(<var>*args</var>)</em></dt> |
| <dd><p>When a convenience function is evaluated, its arguments are converted |
| to instances of <code>gdb.Value</code>, and then the function’s |
| <code>invoke</code> method is called. Note that <small>GDB</small> does not |
| predetermine the arity of convenience functions. Instead, all |
| available arguments are passed to <code>invoke</code>, following the |
| standard Python calling convention. In particular, a convenience |
| function can have default values for parameters without ill effect. |
| </p> |
| <p>The return value of this method is used as its value in the enclosing |
| expression. If an ordinary Python value is returned, it is converted |
| to a <code>gdb.Value</code> following the usual rules. |
| </p></dd></dl> |
| |
| <p>The following code snippet shows how a trivial convenience function can |
| be implemented in Python: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">class Greet (gdb.Function): |
| """Return string to greet someone. |
| Takes a name as argument.""" |
| |
| def __init__ (self): |
| super (Greet, self).__init__ ("greet") |
| |
| def invoke (self, name): |
| return "Hello, %s!" % name.string () |
| |
| Greet () |
| </pre></div> |
| |
| <p>The last line instantiates the class, and is necessary to trigger the |
| registration of the function with <small>GDB</small>. Depending on how the |
| Python code is read into <small>GDB</small>, you may need to import the |
| <code>gdb</code> module explicitly. |
| </p> |
| <p>Now you can use the function in an expression: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) print $greet("Bob") |
| $1 = "Hello, Bob!" |
| </pre></div> |
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