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| <title>Debugging with GDB: Parameters In Python</title> |
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| <a name="Parameters-In-Python"></a> |
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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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| <a name="Parameters-In-Python-1"></a> |
| <h4 class="subsubsection">23.2.2.20 Parameters In Python</h4> |
| |
| <a name="index-parameters-in-python"></a> |
| <a name="index-python-parameters"></a> |
| <a name="index-gdb_002eParameter"></a> |
| <a name="index-Parameter"></a> |
| <p>You can implement new <small>GDB</small> parameters using Python. A new |
| parameter is implemented as an instance of the <code>gdb.Parameter</code> |
| class. |
| </p> |
| <p>Parameters are exposed to the user via the <code>set</code> and |
| <code>show</code> commands. See <a href="Help.html#Help">Help</a>. |
| </p> |
| <p>There are many parameters that already exist and can be set in |
| <small>GDB</small>. Two examples are: <code>set follow fork</code> and |
| <code>set charset</code>. Setting these parameters influences certain |
| behavior in <small>GDB</small>. Similarly, you can define parameters that |
| can be used to influence behavior in custom Python scripts and commands. |
| </p> |
| <dl> |
| <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> |
| <dd><p>The object initializer for <code>Parameter</code> registers the new |
| parameter with <small>GDB</small>. This initializer is normally invoked |
| from the subclass’ own <code>__init__</code> method. |
| </p> |
| <p><var>name</var> is the name of the new parameter. If <var>name</var> consists |
| of multiple words, then the initial words are looked for as prefix |
| parameters. An example of this can be illustrated with the |
| <code>set print</code> set of parameters. If <var>name</var> is |
| <code>print foo</code>, then <code>print</code> will be searched as the prefix |
| parameter. In this case the parameter can subsequently be accessed in |
| <small>GDB</small> as <code>set print foo</code>. |
| </p> |
| <p>If <var>name</var> consists of multiple words, and no prefix parameter group |
| can be found, an exception is raised. |
| </p> |
| <p><var>command-class</var> should be one of the ‘<samp>COMMAND_</samp>’ constants |
| (see <a href="Commands-In-Python.html#Commands-In-Python">Commands In Python</a>). This argument tells <small>GDB</small> how to |
| categorize the new parameter in the help system. |
| </p> |
| <p><var>parameter-class</var> should be one of the ‘<samp>PARAM_</samp>’ constants |
| defined below. This argument tells <small>GDB</small> the type of the new |
| parameter; this information is used for input validation and |
| completion. |
| </p> |
| <p>If <var>parameter-class</var> is <code>PARAM_ENUM</code>, then |
| <var>enum-sequence</var> must be a sequence of strings. These strings |
| represent the possible values for the parameter. |
| </p> |
| <p>If <var>parameter-class</var> is not <code>PARAM_ENUM</code>, then the presence |
| of a fourth argument will cause an exception to be thrown. |
| </p> |
| <p>The help text for the new parameter is taken from the Python |
| documentation string for the parameter’s class, if there is one. If |
| there is no documentation string, a default value is used. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Parameter_002eset_005fdoc"></a>Variable: <strong>Parameter.set_doc</strong></dt> |
| <dd><p>If this attribute exists, and is a string, then its value is used as |
| the help text for this parameter’s <code>set</code> command. The value is |
| examined when <code>Parameter.__init__</code> is invoked; subsequent changes |
| have no effect. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Parameter_002eshow_005fdoc"></a>Variable: <strong>Parameter.show_doc</strong></dt> |
| <dd><p>If this attribute exists, and is a string, then its value is used as |
| the help text for this parameter’s <code>show</code> command. The value is |
| examined when <code>Parameter.__init__</code> is invoked; subsequent changes |
| have no effect. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Parameter_002evalue"></a>Variable: <strong>Parameter.value</strong></dt> |
| <dd><p>The <code>value</code> attribute holds the underlying value of the |
| parameter. It can be read and assigned to just as any other |
| attribute. <small>GDB</small> does validation when assignments are made. |
| </p></dd></dl> |
| |
| <p>There are two methods that should be implemented in any |
| <code>Parameter</code> class. These are: |
| </p> |
| <dl> |
| <dt><a name="index-Parameter_002eget_005fset_005fstring"></a>Function: <strong>Parameter.get_set_string</strong> <em>(self)</em></dt> |
| <dd><p><small>GDB</small> will call this method when a <var>parameter</var>’s value has |
| been changed via the <code>set</code> API (for example, <kbd>set foo off</kbd>). |
| The <code>value</code> attribute has already been populated with the new |
| value and may be used in output. This method must return a string. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Parameter_002eget_005fshow_005fstring"></a>Function: <strong>Parameter.get_show_string</strong> <em>(self, svalue)</em></dt> |
| <dd><p><small>GDB</small> will call this method when a <var>parameter</var>’s |
| <code>show</code> API has been invoked (for example, <kbd>show foo</kbd>). The |
| argument <code>svalue</code> receives the string representation of the |
| current value. This method must return a string. |
| </p></dd></dl> |
| |
| <p>When a new parameter is defined, its type must be specified. The |
| available types are represented by constants defined in the <code>gdb</code> |
| module: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-PARAM_005fBOOLEAN"></a> |
| <a name="index-gdb_002ePARAM_005fBOOLEAN"></a> |
| </dd> |
| <dt><code>gdb.PARAM_BOOLEAN</code></dt> |
| <dd><p>The value is a plain boolean. The Python boolean values, <code>True</code> |
| and <code>False</code> are the only valid values. |
| </p> |
| <a name="index-PARAM_005fAUTO_005fBOOLEAN"></a> |
| <a name="index-gdb_002ePARAM_005fAUTO_005fBOOLEAN"></a> |
| </dd> |
| <dt><code>gdb.PARAM_AUTO_BOOLEAN</code></dt> |
| <dd><p>The value has three possible states: true, false, and ‘<samp>auto</samp>’. In |
| Python, true and false are represented using boolean constants, and |
| ‘<samp>auto</samp>’ is represented using <code>None</code>. |
| </p> |
| <a name="index-PARAM_005fUINTEGER"></a> |
| <a name="index-gdb_002ePARAM_005fUINTEGER"></a> |
| </dd> |
| <dt><code>gdb.PARAM_UINTEGER</code></dt> |
| <dd><p>The value is an unsigned integer. The value of 0 should be |
| interpreted to mean “unlimited”. |
| </p> |
| <a name="index-PARAM_005fINTEGER"></a> |
| <a name="index-gdb_002ePARAM_005fINTEGER"></a> |
| </dd> |
| <dt><code>gdb.PARAM_INTEGER</code></dt> |
| <dd><p>The value is a signed integer. The value of 0 should be interpreted |
| to mean “unlimited”. |
| </p> |
| <a name="index-PARAM_005fSTRING"></a> |
| <a name="index-gdb_002ePARAM_005fSTRING"></a> |
| </dd> |
| <dt><code>gdb.PARAM_STRING</code></dt> |
| <dd><p>The value is a string. When the user modifies the string, any escape |
| sequences, such as ‘<samp>\t</samp>’, ‘<samp>\f</samp>’, and octal escapes, are |
| translated into corresponding characters and encoded into the current |
| host charset. |
| </p> |
| <a name="index-PARAM_005fSTRING_005fNOESCAPE"></a> |
| <a name="index-gdb_002ePARAM_005fSTRING_005fNOESCAPE"></a> |
| </dd> |
| <dt><code>gdb.PARAM_STRING_NOESCAPE</code></dt> |
| <dd><p>The value is a string. When the user modifies the string, escapes are |
| passed through untranslated. |
| </p> |
| <a name="index-PARAM_005fOPTIONAL_005fFILENAME"></a> |
| <a name="index-gdb_002ePARAM_005fOPTIONAL_005fFILENAME"></a> |
| </dd> |
| <dt><code>gdb.PARAM_OPTIONAL_FILENAME</code></dt> |
| <dd><p>The value is a either a filename (a string), or <code>None</code>. |
| </p> |
| <a name="index-PARAM_005fFILENAME"></a> |
| <a name="index-gdb_002ePARAM_005fFILENAME"></a> |
| </dd> |
| <dt><code>gdb.PARAM_FILENAME</code></dt> |
| <dd><p>The value is a filename. This is just like |
| <code>PARAM_STRING_NOESCAPE</code>, but uses file names for completion. |
| </p> |
| <a name="index-PARAM_005fZINTEGER"></a> |
| <a name="index-gdb_002ePARAM_005fZINTEGER"></a> |
| </dd> |
| <dt><code>gdb.PARAM_ZINTEGER</code></dt> |
| <dd><p>The value is an integer. This is like <code>PARAM_INTEGER</code>, except 0 |
| is interpreted as itself. |
| </p> |
| <a name="index-PARAM_005fENUM"></a> |
| <a name="index-gdb_002ePARAM_005fENUM"></a> |
| </dd> |
| <dt><code>gdb.PARAM_ENUM</code></dt> |
| <dd><p>The value is a string, which must be one of a collection string |
| constants provided when the parameter is created. |
| </p></dd> |
| </dl> |
| |
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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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