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299 lines
14 KiB
HTML
299 lines
14 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>Parameters In Python (Debugging with GDB)</title>
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<meta name="description" content="Parameters In Python (Debugging with GDB)">
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<meta name="keywords" content="Parameters 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="Functions-In-Python.html#Functions-In-Python" rel="next" title="Functions In Python">
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<link href="Commands-In-Python.html#Commands-In-Python" rel="prev" title="Commands In Python">
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</head>
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<body lang="en">
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<a name="Parameters-In-Python"></a>
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<div class="header">
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<p>
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Next: <a href="Functions-In-Python.html#Functions-In-Python" accesskey="n" rel="next">Functions In Python</a>, Previous: <a href="Commands-In-Python.html#Commands-In-Python" accesskey="p" rel="prev">Commands 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="Parameters-In-Python-1"></a>
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<h4 class="subsubsection">23.2.2.21 Parameters In Python</h4>
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<a name="index-parameters-in-python"></a>
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<a name="index-python-parameters"></a>
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<a name="index-gdb_002eParameter"></a>
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<a name="index-Parameter"></a>
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<p>You can implement new <small>GDB</small> parameters using Python. A new
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parameter is implemented as an instance of the <code>gdb.Parameter</code>
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class.
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</p>
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<p>Parameters are exposed to the user via the <code>set</code> and
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<code>show</code> commands. See <a href="Help.html#Help">Help</a>.
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</p>
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<p>There are many parameters that already exist and can be set in
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<small>GDB</small>. Two examples are: <code>set follow fork</code> and
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<code>set charset</code>. Setting these parameters influences certain
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behavior in <small>GDB</small>. Similarly, you can define parameters that
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can be used to influence behavior in custom Python scripts and commands.
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</p>
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<dl>
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<dt><a name="index-Parameter_002e_005f_005finit_005f_005f"></a>Function: <strong>Parameter.__init__</strong> <em>(name, <var>command-class</var>, <var>parameter-class</var> <span class="roman">[</span>, <var>enum-sequence</var><span class="roman">]</span>)</em></dt>
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<dd><p>The object initializer for <code>Parameter</code> registers the new
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parameter with <small>GDB</small>. This initializer is normally invoked
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from the subclass’ own <code>__init__</code> method.
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</p>
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<p><var>name</var> is the name of the new parameter. If <var>name</var> consists
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of multiple words, then the initial words are looked for as prefix
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parameters. An example of this can be illustrated with the
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<code>set print</code> set of parameters. If <var>name</var> is
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<code>print foo</code>, then <code>print</code> will be searched as the prefix
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parameter. In this case the parameter can subsequently be accessed in
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<small>GDB</small> as <code>set print foo</code>.
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</p>
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<p>If <var>name</var> consists of multiple words, and no prefix parameter group
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can be found, an exception is raised.
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</p>
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<p><var>command-class</var> should be one of the ‘<samp>COMMAND_</samp>’ constants
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(see <a href="Commands-In-Python.html#Commands-In-Python">Commands In Python</a>). This argument tells <small>GDB</small> how to
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categorize the new parameter in the help system.
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</p>
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<p><var>parameter-class</var> should be one of the ‘<samp>PARAM_</samp>’ constants
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defined below. This argument tells <small>GDB</small> the type of the new
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parameter; this information is used for input validation and
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completion.
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</p>
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<p>If <var>parameter-class</var> is <code>PARAM_ENUM</code>, then
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<var>enum-sequence</var> must be a sequence of strings. These strings
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represent the possible values for the parameter.
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</p>
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<p>If <var>parameter-class</var> is not <code>PARAM_ENUM</code>, then the presence
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of a fourth argument will cause an exception to be thrown.
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</p>
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<p>The help text for the new parameter is taken from the Python
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documentation string for the parameter’s class, if there is one. If
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there is no documentation string, a default value is used.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Parameter_002eset_005fdoc"></a>Variable: <strong>Parameter.set_doc</strong></dt>
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<dd><p>If this attribute exists, and is a string, then its value is used as
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the help text for this parameter’s <code>set</code> command. The value is
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examined when <code>Parameter.__init__</code> is invoked; subsequent changes
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have no effect.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Parameter_002eshow_005fdoc"></a>Variable: <strong>Parameter.show_doc</strong></dt>
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<dd><p>If this attribute exists, and is a string, then its value is used as
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the help text for this parameter’s <code>show</code> command. The value is
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examined when <code>Parameter.__init__</code> is invoked; subsequent changes
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have no effect.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Parameter_002evalue"></a>Variable: <strong>Parameter.value</strong></dt>
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<dd><p>The <code>value</code> attribute holds the underlying value of the
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parameter. It can be read and assigned to just as any other
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attribute. <small>GDB</small> does validation when assignments are made.
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</p></dd></dl>
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<p>There are two methods that may be implemented in any <code>Parameter</code>
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class. These are:
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</p>
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<dl>
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<dt><a name="index-Parameter_002eget_005fset_005fstring"></a>Function: <strong>Parameter.get_set_string</strong> <em>(self)</em></dt>
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<dd><p>If this method exists, <small>GDB</small> will call it when a
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<var>parameter</var>’s value has been changed via the <code>set</code> API (for
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example, <kbd>set foo off</kbd>). The <code>value</code> attribute has already
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been populated with the new value and may be used in output. This
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method must return a string. If the returned string is not empty,
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<small>GDB</small> will present it to the user.
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</p>
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<p>If this method raises the <code>gdb.GdbError</code> exception
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(see <a href="Exception-Handling.html#Exception-Handling">Exception Handling</a>), then <small>GDB</small> will print the
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exception’s string and the <code>set</code> command will fail. Note,
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however, that the <code>value</code> attribute will not be reset in this
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case. So, if your parameter must validate values, it should store the
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old value internally and reset the exposed value, like so:
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</p>
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<div class="smallexample">
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<pre class="smallexample">class ExampleParam (gdb.Parameter):
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def __init__ (self, name):
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super (ExampleParam, self).__init__ (name,
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gdb.COMMAND_DATA,
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gdb.PARAM_BOOLEAN)
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self.value = True
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self.saved_value = True
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def validate(self):
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return False
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def get_set_string (self):
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if not self.validate():
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self.value = self.saved_value
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raise gdb.GdbError('Failed to validate')
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self.saved_value = self.value
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</pre></div>
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</dd></dl>
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<dl>
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<dt><a name="index-Parameter_002eget_005fshow_005fstring"></a>Function: <strong>Parameter.get_show_string</strong> <em>(self, svalue)</em></dt>
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<dd><p><small>GDB</small> will call this method when a <var>parameter</var>’s
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<code>show</code> API has been invoked (for example, <kbd>show foo</kbd>). The
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argument <code>svalue</code> receives the string representation of the
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current value. This method must return a string.
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</p></dd></dl>
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<p>When a new parameter is defined, its type must be specified. The
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available types are represented by constants defined in the <code>gdb</code>
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module:
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</p>
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<dl compact="compact">
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<dd><a name="index-PARAM_005fBOOLEAN"></a>
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<a name="index-gdb_002ePARAM_005fBOOLEAN"></a>
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</dd>
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<dt><code>gdb.PARAM_BOOLEAN</code></dt>
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<dd><p>The value is a plain boolean. The Python boolean values, <code>True</code>
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and <code>False</code> are the only valid values.
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</p>
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<a name="index-PARAM_005fAUTO_005fBOOLEAN"></a>
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<a name="index-gdb_002ePARAM_005fAUTO_005fBOOLEAN"></a>
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</dd>
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<dt><code>gdb.PARAM_AUTO_BOOLEAN</code></dt>
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<dd><p>The value has three possible states: true, false, and ‘<samp>auto</samp>’. In
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Python, true and false are represented using boolean constants, and
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‘<samp>auto</samp>’ is represented using <code>None</code>.
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</p>
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<a name="index-PARAM_005fUINTEGER"></a>
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<a name="index-gdb_002ePARAM_005fUINTEGER"></a>
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</dd>
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<dt><code>gdb.PARAM_UINTEGER</code></dt>
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<dd><p>The value is an unsigned integer. The value of 0 should be
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interpreted to mean “unlimited”.
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</p>
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<a name="index-PARAM_005fINTEGER"></a>
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<a name="index-gdb_002ePARAM_005fINTEGER"></a>
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</dd>
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<dt><code>gdb.PARAM_INTEGER</code></dt>
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<dd><p>The value is a signed integer. The value of 0 should be interpreted
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to mean “unlimited”.
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</p>
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<a name="index-PARAM_005fSTRING"></a>
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<a name="index-gdb_002ePARAM_005fSTRING"></a>
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</dd>
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<dt><code>gdb.PARAM_STRING</code></dt>
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<dd><p>The value is a string. When the user modifies the string, any escape
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sequences, such as ‘<samp>\t</samp>’, ‘<samp>\f</samp>’, and octal escapes, are
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translated into corresponding characters and encoded into the current
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host charset.
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</p>
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<a name="index-PARAM_005fSTRING_005fNOESCAPE"></a>
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<a name="index-gdb_002ePARAM_005fSTRING_005fNOESCAPE"></a>
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</dd>
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<dt><code>gdb.PARAM_STRING_NOESCAPE</code></dt>
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<dd><p>The value is a string. When the user modifies the string, escapes are
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passed through untranslated.
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</p>
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<a name="index-PARAM_005fOPTIONAL_005fFILENAME"></a>
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<a name="index-gdb_002ePARAM_005fOPTIONAL_005fFILENAME"></a>
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</dd>
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<dt><code>gdb.PARAM_OPTIONAL_FILENAME</code></dt>
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<dd><p>The value is a either a filename (a string), or <code>None</code>.
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</p>
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<a name="index-PARAM_005fFILENAME"></a>
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<a name="index-gdb_002ePARAM_005fFILENAME"></a>
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</dd>
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<dt><code>gdb.PARAM_FILENAME</code></dt>
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<dd><p>The value is a filename. This is just like
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<code>PARAM_STRING_NOESCAPE</code>, but uses file names for completion.
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</p>
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<a name="index-PARAM_005fZINTEGER"></a>
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<a name="index-gdb_002ePARAM_005fZINTEGER"></a>
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</dd>
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<dt><code>gdb.PARAM_ZINTEGER</code></dt>
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<dd><p>The value is an integer. This is like <code>PARAM_INTEGER</code>, except 0
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is interpreted as itself.
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</p>
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<a name="index-PARAM_005fZUINTEGER"></a>
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<a name="index-gdb_002ePARAM_005fZUINTEGER"></a>
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</dd>
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<dt><code>gdb.PARAM_ZUINTEGER</code></dt>
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<dd><p>The value is an unsigned integer. This is like <code>PARAM_INTEGER</code>,
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except 0 is interpreted as itself, and the value cannot be negative.
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</p>
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<a name="index-PARAM_005fZUINTEGER_005fUNLIMITED"></a>
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<a name="index-gdb_002ePARAM_005fZUINTEGER_005fUNLIMITED"></a>
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</dd>
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<dt><code>gdb.PARAM_ZUINTEGER_UNLIMITED</code></dt>
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<dd><p>The value is a signed integer. This is like <code>PARAM_ZUINTEGER</code>,
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except the special value -1 should be interpreted to mean
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“unlimited”. Other negative values are not allowed.
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</p>
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<a name="index-PARAM_005fENUM"></a>
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<a name="index-gdb_002ePARAM_005fENUM"></a>
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</dd>
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<dt><code>gdb.PARAM_ENUM</code></dt>
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<dd><p>The value is a string, which must be one of a collection string
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constants provided when the parameter is created.
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</p></dd>
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</dl>
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<hr>
|
||
|
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<div class="header">
|
||
|
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<p>
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