1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with the 8Invariant Sections being "Free Software" and "Free Software Needs 9Free Documentation", with the Front-Cover Texts being "A GNU Manual," 10and with the Back-Cover Texts as in (a) below. 11 12(a) The FSF's Back-Cover Text is: "You are free to copy and modify 13this GNU Manual. 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A new 78parameter is implemented as an instance of the <code>gdb.Parameter</code> 79class. 80</p> 81<p>Parameters are exposed to the user via the <code>set</code> and 82<code>show</code> commands. See <a href="Help.html#Help">Help</a>. 83</p> 84<p>There are many parameters that already exist and can be set in 85<small>GDB</small>. Two examples are: <code>set follow fork</code> and 86<code>set charset</code>. Setting these parameters influences certain 87behavior in <small>GDB</small>. Similarly, you can define parameters that 88can be used to influence behavior in custom Python scripts and commands. 89</p> 90<dl> 91<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> 92<dd><p>The object initializer for <code>Parameter</code> registers the new 93parameter with <small>GDB</small>. This initializer is normally invoked 94from the subclass’ own <code>__init__</code> method. 95</p> 96<p><var>name</var> is the name of the new parameter. If <var>name</var> consists 97of multiple words, then the initial words are looked for as prefix 98parameters. An example of this can be illustrated with the 99<code>set print</code> set of parameters. If <var>name</var> is 100<code>print foo</code>, then <code>print</code> will be searched as the prefix 101parameter. In this case the parameter can subsequently be accessed in 102<small>GDB</small> as <code>set print foo</code>. 103</p> 104<p>If <var>name</var> consists of multiple words, and no prefix parameter group 105can be found, an exception is raised. 106</p> 107<p><var>command-class</var> should be one of the ‘<samp>COMMAND_</samp>’ constants 108(see <a href="Commands-In-Python.html#Commands-In-Python">Commands In Python</a>). This argument tells <small>GDB</small> how to 109categorize the new parameter in the help system. 110</p> 111<p><var>parameter-class</var> should be one of the ‘<samp>PARAM_</samp>’ constants 112defined below. This argument tells <small>GDB</small> the type of the new 113parameter; this information is used for input validation and 114completion. 115</p> 116<p>If <var>parameter-class</var> is <code>PARAM_ENUM</code>, then 117<var>enum-sequence</var> must be a sequence of strings. These strings 118represent the possible values for the parameter. 119</p> 120<p>If <var>parameter-class</var> is not <code>PARAM_ENUM</code>, then the presence 121of a fourth argument will cause an exception to be thrown. 122</p> 123<p>The help text for the new parameter is taken from the Python 124documentation string for the parameter’s class, if there is one. If 125there is no documentation string, a default value is used. 126</p></dd></dl> 127 128<dl> 129<dt><a name="index-Parameter_002eset_005fdoc"></a>Variable: <strong>Parameter.set_doc</strong></dt> 130<dd><p>If this attribute exists, and is a string, then its value is used as 131the help text for this parameter’s <code>set</code> command. The value is 132examined when <code>Parameter.__init__</code> is invoked; subsequent changes 133have no effect. 134</p></dd></dl> 135 136<dl> 137<dt><a name="index-Parameter_002eshow_005fdoc"></a>Variable: <strong>Parameter.show_doc</strong></dt> 138<dd><p>If this attribute exists, and is a string, then its value is used as 139the help text for this parameter’s <code>show</code> command. The value is 140examined when <code>Parameter.__init__</code> is invoked; subsequent changes 141have no effect. 142</p></dd></dl> 143 144<dl> 145<dt><a name="index-Parameter_002evalue"></a>Variable: <strong>Parameter.value</strong></dt> 146<dd><p>The <code>value</code> attribute holds the underlying value of the 147parameter. It can be read and assigned to just as any other 148attribute. <small>GDB</small> does validation when assignments are made. 149</p></dd></dl> 150 151<p>There are two methods that may be implemented in any <code>Parameter</code> 152class. These are: 153</p> 154<dl> 155<dt><a name="index-Parameter_002eget_005fset_005fstring"></a>Function: <strong>Parameter.get_set_string</strong> <em>(self)</em></dt> 156<dd><p>If this method exists, <small>GDB</small> will call it when a 157<var>parameter</var>’s value has been changed via the <code>set</code> API (for 158example, <kbd>set foo off</kbd>). The <code>value</code> attribute has already 159been populated with the new value and may be used in output. This 160method must return a string. If the returned string is not empty, 161<small>GDB</small> will present it to the user. 162</p> 163<p>If this method raises the <code>gdb.GdbError</code> exception 164(see <a href="Exception-Handling.html#Exception-Handling">Exception Handling</a>), then <small>GDB</small> will print the 165exception’s string and the <code>set</code> command will fail. Note, 166however, that the <code>value</code> attribute will not be reset in this 167case. So, if your parameter must validate values, it should store the 168old value internally and reset the exposed value, like so: 169</p> 170<div class="smallexample"> 171<pre class="smallexample">class ExampleParam (gdb.Parameter): 172 def __init__ (self, name): 173 super (ExampleParam, self).__init__ (name, 174 gdb.COMMAND_DATA, 175 gdb.PARAM_BOOLEAN) 176 self.value = True 177 self.saved_value = True 178 def validate(self): 179 return False 180 def get_set_string (self): 181 if not self.validate(): 182 self.value = self.saved_value 183 raise gdb.GdbError('Failed to validate') 184 self.saved_value = self.value 185</pre></div> 186</dd></dl> 187 188<dl> 189<dt><a name="index-Parameter_002eget_005fshow_005fstring"></a>Function: <strong>Parameter.get_show_string</strong> <em>(self, svalue)</em></dt> 190<dd><p><small>GDB</small> will call this method when a <var>parameter</var>’s 191<code>show</code> API has been invoked (for example, <kbd>show foo</kbd>). The 192argument <code>svalue</code> receives the string representation of the 193current value. This method must return a string. 194</p></dd></dl> 195 196<p>When a new parameter is defined, its type must be specified. The 197available types are represented by constants defined in the <code>gdb</code> 198module: 199</p> 200<dl compact="compact"> 201<dd><a name="index-PARAM_005fBOOLEAN"></a> 202<a name="index-gdb_002ePARAM_005fBOOLEAN"></a> 203</dd> 204<dt><code>gdb.PARAM_BOOLEAN</code></dt> 205<dd><p>The value is a plain boolean. The Python boolean values, <code>True</code> 206and <code>False</code> are the only valid values. 207</p> 208<a name="index-PARAM_005fAUTO_005fBOOLEAN"></a> 209<a name="index-gdb_002ePARAM_005fAUTO_005fBOOLEAN"></a> 210</dd> 211<dt><code>gdb.PARAM_AUTO_BOOLEAN</code></dt> 212<dd><p>The value has three possible states: true, false, and ‘<samp>auto</samp>’. In 213Python, true and false are represented using boolean constants, and 214‘<samp>auto</samp>’ is represented using <code>None</code>. 215</p> 216<a name="index-PARAM_005fUINTEGER"></a> 217<a name="index-gdb_002ePARAM_005fUINTEGER"></a> 218</dd> 219<dt><code>gdb.PARAM_UINTEGER</code></dt> 220<dd><p>The value is an unsigned integer. The value of 0 should be 221interpreted to mean “unlimited”. 222</p> 223<a name="index-PARAM_005fINTEGER"></a> 224<a name="index-gdb_002ePARAM_005fINTEGER"></a> 225</dd> 226<dt><code>gdb.PARAM_INTEGER</code></dt> 227<dd><p>The value is a signed integer. The value of 0 should be interpreted 228to mean “unlimited”. 229</p> 230<a name="index-PARAM_005fSTRING"></a> 231<a name="index-gdb_002ePARAM_005fSTRING"></a> 232</dd> 233<dt><code>gdb.PARAM_STRING</code></dt> 234<dd><p>The value is a string. When the user modifies the string, any escape 235sequences, such as ‘<samp>\t</samp>’, ‘<samp>\f</samp>’, and octal escapes, are 236translated into corresponding characters and encoded into the current 237host charset. 238</p> 239<a name="index-PARAM_005fSTRING_005fNOESCAPE"></a> 240<a name="index-gdb_002ePARAM_005fSTRING_005fNOESCAPE"></a> 241</dd> 242<dt><code>gdb.PARAM_STRING_NOESCAPE</code></dt> 243<dd><p>The value is a string. When the user modifies the string, escapes are 244passed through untranslated. 245</p> 246<a name="index-PARAM_005fOPTIONAL_005fFILENAME"></a> 247<a name="index-gdb_002ePARAM_005fOPTIONAL_005fFILENAME"></a> 248</dd> 249<dt><code>gdb.PARAM_OPTIONAL_FILENAME</code></dt> 250<dd><p>The value is a either a filename (a string), or <code>None</code>. 251</p> 252<a name="index-PARAM_005fFILENAME"></a> 253<a name="index-gdb_002ePARAM_005fFILENAME"></a> 254</dd> 255<dt><code>gdb.PARAM_FILENAME</code></dt> 256<dd><p>The value is a filename. This is just like 257<code>PARAM_STRING_NOESCAPE</code>, but uses file names for completion. 258</p> 259<a name="index-PARAM_005fZINTEGER"></a> 260<a name="index-gdb_002ePARAM_005fZINTEGER"></a> 261</dd> 262<dt><code>gdb.PARAM_ZINTEGER</code></dt> 263<dd><p>The value is an integer. This is like <code>PARAM_INTEGER</code>, except 0 264is interpreted as itself. 265</p> 266<a name="index-PARAM_005fZUINTEGER"></a> 267<a name="index-gdb_002ePARAM_005fZUINTEGER"></a> 268</dd> 269<dt><code>gdb.PARAM_ZUINTEGER</code></dt> 270<dd><p>The value is an unsigned integer. This is like <code>PARAM_INTEGER</code>, 271except 0 is interpreted as itself, and the value cannot be negative. 272</p> 273<a name="index-PARAM_005fZUINTEGER_005fUNLIMITED"></a> 274<a name="index-gdb_002ePARAM_005fZUINTEGER_005fUNLIMITED"></a> 275</dd> 276<dt><code>gdb.PARAM_ZUINTEGER_UNLIMITED</code></dt> 277<dd><p>The value is a signed integer. This is like <code>PARAM_ZUINTEGER</code>, 278except the special value -1 should be interpreted to mean 279“unlimited”. Other negative values are not allowed. 280</p> 281<a name="index-PARAM_005fENUM"></a> 282<a name="index-gdb_002ePARAM_005fENUM"></a> 283</dd> 284<dt><code>gdb.PARAM_ENUM</code></dt> 285<dd><p>The value is a string, which must be one of a collection string 286constants provided when the parameter is created. 287</p></dd> 288</dl> 289 290<hr> 291<div class="header"> 292<p> 293Next: <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="previous">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> 294</div> 295 296 297 298</body> 299</html> 300