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| <h5 class="subsubsection">23.2.2.21 Parameters In Python</h5> |
| |
| <p><a name="index-parameters-in-python-2183"></a><a name="index-python-parameters-2184"></a><a name="index-gdb_002eParameter-2185"></a><a name="index-Parameter-2186"></a>You can implement new <span class="sc">gdb</span> parameters using Python. A new |
| parameter is implemented as an instance of the <code>gdb.Parameter</code> |
| class. |
| |
| <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>There are many parameters that already exist and can be set in |
| <span class="sc">gdb</span>. Two examples are: <code>set follow fork</code> and |
| <code>set charset</code>. Setting these parameters influences certain |
| behavior in <span class="sc">gdb</span>. Similarly, you can define parameters that |
| can be used to influence behavior in custom Python scripts and commands. |
| |
| <div class="defun"> |
| — Function: <b>Parameter.__init__</b> (<var>name, command-class, parameter-class </var><span class="roman">[</span><var>, enum-sequence</var><span class="roman">]</span>)<var><a name="index-Parameter_002e_005f_005finit_005f_005f-2187"></a></var><br> |
| <blockquote><p>The object initializer for <code>Parameter</code> registers the new |
| parameter with <span class="sc">gdb</span>. This initializer is normally invoked |
| from the subclass' own <code>__init__</code> method. |
| |
| <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 |
| <span class="sc">gdb</span> as <code>set print foo</code>. |
| |
| <p>If <var>name</var> consists of multiple words, and no prefix parameter group |
| can be found, an exception is raised. |
| |
| <p><var>command-class</var> should be one of the ‘<samp><span class="samp">COMMAND_</span></samp>’ constants |
| (see <a href="Commands-In-Python.html#Commands-In-Python">Commands In Python</a>). This argument tells <span class="sc">gdb</span> how to |
| categorize the new parameter in the help system. |
| |
| <p><var>parameter-class</var> should be one of the ‘<samp><span class="samp">PARAM_</span></samp>’ constants |
| defined below. This argument tells <span class="sc">gdb</span> the type of the new |
| parameter; this information is used for input validation and |
| completion. |
| |
| <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>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>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></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Parameter.set_doc</b><var><a name="index-Parameter_002eset_005fdoc-2188"></a></var><br> |
| <blockquote><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></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Parameter.show_doc</b><var><a name="index-Parameter_002eshow_005fdoc-2189"></a></var><br> |
| <blockquote><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></blockquote></div> |
| |
| <div class="defun"> |
| — Variable: <b>Parameter.value</b><var><a name="index-Parameter_002evalue-2190"></a></var><br> |
| <blockquote><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. <span class="sc">gdb</span> does validation when assignments are made. |
| </p></blockquote></div> |
| |
| <p>There are two methods that may be implemented in any <code>Parameter</code> |
| class. These are: |
| |
| <div class="defun"> |
| — Function: <b>Parameter.get_set_string</b> (<var>self</var>)<var><a name="index-Parameter_002eget_005fset_005fstring-2191"></a></var><br> |
| <blockquote><p>If this method exists, <span class="sc">gdb</span> will call it 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. If the returned string is not empty, |
| <span class="sc">gdb</span> will present it to the user. |
| |
| <p>If this method raises the <code>gdb.GdbError</code> exception |
| (see <a href="Exception-Handling.html#Exception-Handling">Exception Handling</a>), then <span class="sc">gdb</span> will print the |
| exception's string and the <code>set</code> command will fail. Note, |
| however, that the <code>value</code> attribute will not be reset in this |
| case. So, if your parameter must validate values, it should store the |
| old value internally and reset the exposed value, like so: |
| |
| <pre class="smallexample"> class ExampleParam (gdb.Parameter): |
| def __init__ (self, name): |
| super (ExampleParam, self).__init__ (name, |
| gdb.COMMAND_DATA, |
| gdb.PARAM_BOOLEAN) |
| self.value = True |
| self.saved_value = True |
| def validate(self): |
| return False |
| def get_set_string (self): |
| if not self.validate(): |
| self.value = self.saved_value |
| raise gdb.GdbError('Failed to validate') |
| self.saved_value = self.value |
| </pre> |
| </blockquote></div> |
| |
| <div class="defun"> |
| — Function: <b>Parameter.get_show_string</b> (<var>self, svalue</var>)<var><a name="index-Parameter_002eget_005fshow_005fstring-2192"></a></var><br> |
| <blockquote><p><span class="sc">gdb</span> 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></blockquote></div> |
| |
| <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: |
| |
| |
| <a name="index-PARAM_005fBOOLEAN-2193"></a> |
| <a name="index-gdb_002ePARAM_005fBOOLEAN-2194"></a> |
| <dl><dt><code>gdb.PARAM_BOOLEAN</code><dd>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-2195"></a><a name="index-gdb_002ePARAM_005fAUTO_005fBOOLEAN-2196"></a><br><dt><code>gdb.PARAM_AUTO_BOOLEAN</code><dd>The value has three possible states: true, false, and ‘<samp><span class="samp">auto</span></samp>’. In |
| Python, true and false are represented using boolean constants, and |
| ‘<samp><span class="samp">auto</span></samp>’ is represented using <code>None</code>. |
| |
| <p><a name="index-PARAM_005fUINTEGER-2197"></a><a name="index-gdb_002ePARAM_005fUINTEGER-2198"></a><br><dt><code>gdb.PARAM_UINTEGER</code><dd>The value is an unsigned integer. The value of 0 should be |
| interpreted to mean “unlimited”. |
| |
| <p><a name="index-PARAM_005fINTEGER-2199"></a><a name="index-gdb_002ePARAM_005fINTEGER-2200"></a><br><dt><code>gdb.PARAM_INTEGER</code><dd>The value is a signed integer. The value of 0 should be interpreted |
| to mean “unlimited”. |
| |
| <p><a name="index-PARAM_005fSTRING-2201"></a><a name="index-gdb_002ePARAM_005fSTRING-2202"></a><br><dt><code>gdb.PARAM_STRING</code><dd>The value is a string. When the user modifies the string, any escape |
| sequences, such as ‘<samp><span class="samp">\t</span></samp>’, ‘<samp><span class="samp">\f</span></samp>’, and octal escapes, are |
| translated into corresponding characters and encoded into the current |
| host charset. |
| |
| <p><a name="index-PARAM_005fSTRING_005fNOESCAPE-2203"></a><a name="index-gdb_002ePARAM_005fSTRING_005fNOESCAPE-2204"></a><br><dt><code>gdb.PARAM_STRING_NOESCAPE</code><dd>The value is a string. When the user modifies the string, escapes are |
| passed through untranslated. |
| |
| <p><a name="index-PARAM_005fOPTIONAL_005fFILENAME-2205"></a><a name="index-gdb_002ePARAM_005fOPTIONAL_005fFILENAME-2206"></a><br><dt><code>gdb.PARAM_OPTIONAL_FILENAME</code><dd>The value is a either a filename (a string), or <code>None</code>. |
| |
| <p><a name="index-PARAM_005fFILENAME-2207"></a><a name="index-gdb_002ePARAM_005fFILENAME-2208"></a><br><dt><code>gdb.PARAM_FILENAME</code><dd>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-2209"></a><a name="index-gdb_002ePARAM_005fZINTEGER-2210"></a><br><dt><code>gdb.PARAM_ZINTEGER</code><dd>The value is an integer. This is like <code>PARAM_INTEGER</code>, except 0 |
| is interpreted as itself. |
| |
| <p><a name="index-PARAM_005fZUINTEGER-2211"></a><a name="index-gdb_002ePARAM_005fZUINTEGER-2212"></a><br><dt><code>gdb.PARAM_ZUINTEGER</code><dd>The value is an unsigned integer. This is like <code>PARAM_INTEGER</code>, |
| except 0 is interpreted as itself, and the value cannot be negative. |
| |
| <p><a name="index-PARAM_005fZUINTEGER_005fUNLIMITED-2213"></a><a name="index-gdb_002ePARAM_005fZUINTEGER_005fUNLIMITED-2214"></a><br><dt><code>gdb.PARAM_ZUINTEGER_UNLIMITED</code><dd>The value is a signed integer. This is like <code>PARAM_ZUINTEGER</code>, |
| except the special value -1 should be interpreted to mean |
| “unlimited”. Other negative values are not allowed. |
| |
| <p><a name="index-PARAM_005fENUM-2215"></a><a name="index-gdb_002ePARAM_005fENUM-2216"></a><br><dt><code>gdb.PARAM_ENUM</code><dd>The value is a string, which must be one of a collection string |
| constants provided when the parameter is created. |
| </dl> |
| |
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| |
