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| <h5 class="subsubsection">23.2.2.22 Writing new convenience functions</h5> |
| |
| <p><a name="index-writing-convenience-functions-2217"></a><a name="index-convenience-functions-in-python-2218"></a><a name="index-python-convenience-functions-2219"></a><a name="index-gdb_002eFunction-2220"></a><a name="index-Function-2221"></a>You can implement new convenience functions (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>) |
| in Python. A convenience function is an instance of a subclass of the |
| class <code>gdb.Function</code>. |
| |
| <div class="defun"> |
| — Function: <b>Function.__init__</b> (<var>name</var>)<var><a name="index-Function_002e_005f_005finit_005f_005f-2222"></a></var><br> |
| <blockquote><p>The initializer for <code>Function</code> registers the new function with |
| <span class="sc">gdb</span>. The argument <var>name</var> is the name of the function, |
| a string. The function will be visible to the user as a convenience |
| variable of type <code>internal function</code>, whose name is the same as |
| the given <var>name</var>. |
| |
| <p>The documentation for the new function is taken from the documentation |
| string for the new class. |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Function: <b>Function.invoke</b> (<var>*args</var>)<var><a name="index-Function_002einvoke-2223"></a></var><br> |
| <blockquote><p>When a convenience function is evaluated, its arguments are converted |
| to instances of <code>gdb.Value</code>, and then the function's |
| <code>invoke</code> method is called. Note that <span class="sc">gdb</span> does not |
| predetermine the arity of convenience functions. Instead, all |
| available arguments are passed to <code>invoke</code>, following the |
| standard Python calling convention. In particular, a convenience |
| function can have default values for parameters without ill effect. |
| |
| <p>The return value of this method is used as its value in the enclosing |
| expression. If an ordinary Python value is returned, it is converted |
| to a <code>gdb.Value</code> following the usual rules. |
| </p></blockquote></div> |
| |
| <p>The following code snippet shows how a trivial convenience function can |
| be implemented in Python: |
| |
| <pre class="smallexample"> class Greet (gdb.Function): |
| """Return string to greet someone. |
| Takes a name as argument.""" |
| |
| def __init__ (self): |
| super (Greet, self).__init__ ("greet") |
| |
| def invoke (self, name): |
| return "Hello, %s!" % name.string () |
| |
| Greet () |
| </pre> |
| <p>The last line instantiates the class, and is necessary to trigger the |
| registration of the function with <span class="sc">gdb</span>. Depending on how the |
| Python code is read into <span class="sc">gdb</span>, you may need to import the |
| <code>gdb</code> module explicitly. |
| |
| <p>Now you can use the function in an expression: |
| |
| <pre class="smallexample"> (gdb) print $greet("Bob") |
| $1 = "Hello, Bob!" |
| </pre> |
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