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147 lines
6.6 KiB
HTML
147 lines
6.6 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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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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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Functions In Python (Debugging with GDB)</title>
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<meta name="description" content="Functions In Python (Debugging with GDB)">
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<meta name="keywords" content="Functions In Python (Debugging with GDB)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Python-API.html#Python-API" rel="up" title="Python API">
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<link href="Progspaces-In-Python.html#Progspaces-In-Python" rel="next" title="Progspaces In Python">
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<link href="Parameters-In-Python.html#Parameters-In-Python" rel="prev" title="Parameters In Python">
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</style>
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</head>
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<body lang="en">
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<a name="Functions-In-Python"></a>
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<div class="header">
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<p>
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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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</div>
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<hr>
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<a name="Writing-new-convenience-functions"></a>
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<h4 class="subsubsection">23.2.2.22 Writing new convenience functions</h4>
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<a name="index-writing-convenience-functions"></a>
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<a name="index-convenience-functions-in-python"></a>
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<a name="index-python-convenience-functions"></a>
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<a name="index-gdb_002eFunction"></a>
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<a name="index-Function"></a>
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<p>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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</p>
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<dl>
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<dt><a name="index-Function_002e_005f_005finit_005f_005f"></a>Function: <strong>Function.__init__</strong> <em>(name)</em></dt>
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<dd><p>The initializer for <code>Function</code> registers the new function with
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<small>GDB</small>. 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>
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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></dd></dl>
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<dl>
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<dt><a name="index-Function_002einvoke"></a>Function: <strong>Function.invoke</strong> <em>(<var>*args</var>)</em></dt>
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<dd><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 <small>GDB</small> 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>
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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></dd></dl>
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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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</p>
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<div class="smallexample">
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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></div>
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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 <small>GDB</small>. Depending on how the
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Python code is read into <small>GDB</small>, you may need to import the
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<code>gdb</code> module explicitly.
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</p>
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<p>Now you can use the function in an expression:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print $greet("Bob")
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$1 = "Hello, Bob!"
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</pre></div>
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<hr>
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<div class="header">
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<p>
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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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</div>
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</body>
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</html>
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