109 lines
5.1 KiB
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109 lines
5.1 KiB
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<title>Functions In Python - Debugging with GDB</title>
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<link rel="up" href="Python-API.html#Python-API" title="Python API">
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<link rel="prev" href="Parameters-In-Python.html#Parameters-In-Python" title="Parameters In Python">
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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<div class="node">
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<a name="Functions-In-Python"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Progspaces-In-Python.html#Progspaces-In-Python">Progspaces In Python</a>,
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Previous: <a rel="previous" accesskey="p" href="Parameters-In-Python.html#Parameters-In-Python">Parameters In Python</a>,
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Up: <a rel="up" accesskey="u" href="Python-API.html#Python-API">Python API</a>
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<hr>
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</div>
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<h5 class="subsubsection">23.2.2.22 Writing new convenience functions</h5>
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<p><a name="index-writing-convenience-functions-2217"></a><a name="index-convenience-functions-in-python-2218"></a><a name="index-python-convenience-functions-2219"></a><a name="index-gdb_002eFunction-2220"></a><a name="index-Function-2221"></a>You can implement new convenience functions (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>)
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in Python. A convenience function is an instance of a subclass of the
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class <code>gdb.Function</code>.
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<div class="defun">
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— Function: <b>Function.__init__</b> (<var>name</var>)<var><a name="index-Function_002e_005f_005finit_005f_005f-2222"></a></var><br>
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<blockquote><p>The initializer for <code>Function</code> registers the new function with
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<span class="sc">gdb</span>. The argument <var>name</var> is the name of the function,
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a string. The function will be visible to the user as a convenience
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variable of type <code>internal function</code>, whose name is the same as
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the given <var>name</var>.
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<p>The documentation for the new function is taken from the documentation
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string for the new class.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Function.invoke</b> (<var>*args</var>)<var><a name="index-Function_002einvoke-2223"></a></var><br>
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<blockquote><p>When a convenience function is evaluated, its arguments are converted
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to instances of <code>gdb.Value</code>, and then the function's
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<code>invoke</code> method is called. Note that <span class="sc">gdb</span> does not
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predetermine the arity of convenience functions. Instead, all
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available arguments are passed to <code>invoke</code>, following the
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standard Python calling convention. In particular, a convenience
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function can have default values for parameters without ill effect.
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<p>The return value of this method is used as its value in the enclosing
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expression. If an ordinary Python value is returned, it is converted
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to a <code>gdb.Value</code> following the usual rules.
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</p></blockquote></div>
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<p>The following code snippet shows how a trivial convenience function can
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be implemented in Python:
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<pre class="smallexample"> class Greet (gdb.Function):
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"""Return string to greet someone.
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Takes a name as argument."""
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def __init__ (self):
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super (Greet, self).__init__ ("greet")
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def invoke (self, name):
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return "Hello, %s!" % name.string ()
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Greet ()
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</pre>
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<p>The last line instantiates the class, and is necessary to trigger the
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registration of the function with <span class="sc">gdb</span>. Depending on how the
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Python code is read into <span class="sc">gdb</span>, you may need to import the
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<code>gdb</code> module explicitly.
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<p>Now you can use the function in an expression:
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<pre class="smallexample"> (gdb) print $greet("Bob")
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$1 = "Hello, Bob!"
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</pre>
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</body></html>
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