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<title>Debugging with GDB: GDB/MI Commands In Python</title>
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<a name="GDB_002fMI-Commands-In-Python"></a>
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<p>
Next: <a href="Parameters-In-Python.html#Parameters-In-Python" accesskey="n" rel="next">Parameters In Python</a>, Previous: <a href="CLI-Commands-In-Python.html#CLI-Commands-In-Python" accesskey="p" rel="previous">CLI 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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<hr>
<a name="GDB_002fMI-Commands-In-Python-1"></a>
<h4 class="subsubsection">23.3.2.21 <small>GDB/MI</small> Commands In Python</h4>
<a name="index-MI-commands-in-python"></a>
<a name="index-commands-in-python_002c-GDB_002fMI"></a>
<a name="index-python-commands_002c-GDB_002fMI"></a>
<p>It is possible to add <small>GDB/MI</small> (see <a href="GDB_002fMI.html#GDB_002fMI">GDB/MI</a>) commands
implemented in Python. A <small>GDB/MI</small> command is implemented using an
instance of the <code>gdb.MICommand</code> class, most commonly using a
subclass.
</p>
<dl>
<dt><a name="index-MICommand_002e_005f_005finit_005f_005f"></a>Function: <strong>MICommand.__init__</strong> <em>(name)</em></dt>
<dd><p>The object initializer for <code>MICommand</code> registers the new command
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 command. It must be a valid name of a
<small>GDB/MI</small> command, and in particular must start with a hyphen
(<code>-</code>). Reusing the name of a built-in <small>GDB/MI</small> is not
allowed, and a <code>RuntimeError</code> will be raised. Using the name
of an <small>GDB/MI</small> command previously defined in Python is allowed, the
previous command will be replaced with the new command.
</p></dd></dl>
<dl>
<dt><a name="index-MICommand_002einvoke"></a>Function: <strong>MICommand.invoke</strong> <em>(arguments)</em></dt>
<dd><p>This method is called by <small>GDB</small> when the new MI command is
invoked.
</p>
<p><var>arguments</var> is a list of strings. Note, that <code>--thread</code>
and <code>--frame</code> arguments are handled by <small>GDB</small> itself therefore
they do not show up in <code>arguments</code>.
</p>
<p>If this method raises an exception, then it is turned into a
<small>GDB/MI</small> <code>^error</code> response. Only <code>gdb.GdbError</code>
exceptions (or its sub-classes) should be used for reporting errors to
users, any other exception type is treated as a failure of the
<code>invoke</code> method, and the exception will be printed to the error
stream according to the <kbd>set python print-stack</kbd> setting
(see <a href="Python-Commands.html#set_005fpython_005fprint_005fstack"><kbd>set python print-stack</kbd></a>).
</p>
<p>If this method returns <code>None</code>, then the <small>GDB/MI</small> command will
return a <code>^done</code> response with no additional values.
</p>
<p>Otherwise, the return value must be a dictionary, which is converted
to a <small>GDB/MI</small> <var>result-record</var> (see <a href="GDB_002fMI-Output-Syntax.html#GDB_002fMI-Output-Syntax">GDB/MI Output Syntax</a>).
The keys of this dictionary must be strings, and are used as
<var>variable</var> names in the <var>result-record</var>, these strings must
comply with the naming rules detailed below. The values of this
dictionary are recursively handled as follows:
</p>
<ul>
<li> If the value is Python sequence or iterator, it is converted to
<small>GDB/MI</small> <var>list</var> with elements converted recursively.
</li><li> If the value is Python dictionary, it is converted to
<small>GDB/MI</small> <var>tuple</var>. Keys in that dictionary must be strings,
which comply with the <var>variable</var> naming rules detailed below.
Values are converted recursively.
</li><li> Otherwise, value is first converted to a Python string using
<code>str ()</code> and then converted to <small>GDB/MI</small> <var>const</var>.
</li></ul>
<p>The strings used for <var>variable</var> names in the <small>GDB/MI</small> output
must follow the following rules; the string must be at least one
character long, the first character must be in the set
<code>[a-zA-Z]</code>, while every subsequent character must be in the set
<code>[-_a-zA-Z0-9]</code>.
</p></dd></dl>
<p>An instance of <code>MICommand</code> has the following attributes:
</p>
<dl>
<dt><a name="index-MICommand_002ename"></a>Variable: <strong>MICommand.name</strong></dt>
<dd><p>A string, the name of this <small>GDB/MI</small> command, as was passed to the
<code>__init__</code> method. This attribute is read-only.
</p></dd></dl>
<dl>
<dt><a name="index-MICommand_002einstalled"></a>Variable: <strong>MICommand.installed</strong></dt>
<dd><p>A boolean value indicating if this command is installed ready for a
user to call from the command line. Commands are automatically
installed when they are instantiated, after which this attribute will
be <code>True</code>.
</p>
<p>If later, a new command is created with the same name, then the
original command will become uninstalled, and this attribute will be
<code>False</code>.
</p>
<p>This attribute is read-write, setting this attribute to <code>False</code>
will uninstall the command, removing it from the set of available
commands. Setting this attribute to <code>True</code> will install the
command for use. If there is already a Python command with this name
installed, the currently installed command will be uninstalled, and
this command installed in its place.
</p></dd></dl>
<p>The following code snippet shows how a two trivial MI command can be
implemented in Python:
</p>
<div class="smallexample">
<pre class="smallexample">class MIEcho(gdb.MICommand):
"""Echo arguments passed to the command."""
def __init__(self, name, mode):
self._mode = mode
super(MIEcho, self).__init__(name)
def invoke(self, argv):
if self._mode == 'dict':
return { 'dict': { 'argv' : argv } }
elif self._mode == 'list':
return { 'list': argv }
else:
return { 'string': ", ".join(argv) }
MIEcho("-echo-dict", "dict")
MIEcho("-echo-list", "list")
MIEcho("-echo-string", "string")
</pre></div>
<p>The last three lines instantiate the class three times, creating three
new <small>GDB/MI</small> commands <code>-echo-dict</code>, <code>-echo-list</code>, and
<code>-echo-string</code>. Each time a subclass of <code>gdb.MICommand</code> is
instantiated, the new command is automatically registered with
<small>GDB</small>.
</p>
<p>Depending on how the Python code is read into <small>GDB</small>, you may
need to import the <code>gdb</code> module explicitly.
</p>
<p>The following example shows a <small>GDB</small> session in which the above
commands have been added:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb)
-echo-dict abc def ghi
^done,dict={argv=["abc","def","ghi"]}
(gdb)
-echo-list abc def ghi
^done,list=["abc","def","ghi"]
(gdb)
-echo-string abc def ghi
^done,string="abc, def, ghi"
(gdb)
</pre></div>
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Next: <a href="Parameters-In-Python.html#Parameters-In-Python" accesskey="n" rel="next">Parameters In Python</a>, Previous: <a href="CLI-Commands-In-Python.html#CLI-Commands-In-Python" accesskey="p" rel="previous">CLI 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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