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<h5 class="subsubsection">23.2.2.26 Accessing blocks from Python</h5>

<p><a name="index-blocks-in-python-2286"></a><a name="index-gdb_002eBlock-2287"></a>
In <span class="sc">gdb</span>, symbols are stored in blocks.  A block corresponds
roughly to a scope in the source code.  Blocks are organized
hierarchically, and are represented individually in Python as a
<code>gdb.Block</code>.  Blocks rely on debugging information being
available.

   <p>A frame has a block.  Please see <a href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>, for a more
in-depth discussion of frames.

   <p>The outermost block is known as the <dfn>global block</dfn>.  The global
block typically holds public global variables and functions.

   <p>The block nested just inside the global block is the <dfn>static
block</dfn>.  The static block typically holds file-scoped variables and
functions.

   <p><span class="sc">gdb</span> provides a method to get a block's superblock, but there
is currently no way to examine the sub-blocks of a block, or to
iterate over all the blocks in a symbol table (see <a href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python">Symbol Tables In Python</a>).

   <p>Here is a short example that should help explain blocks:

<pre class="smallexample">     /* This is in the global block.  */
     int global;
     
     /* This is in the static block.  */
     static int file_scope;
     
     /* 'function' is in the global block, and 'argument' is
        in a block nested inside of 'function'.  */
     int function (int argument)
     {
       /* 'local' is in a block inside 'function'.  It may or may
          not be in the same block as 'argument'.  */
       int local;
     
       {
          /* 'inner' is in a block whose superblock is the one holding
             'local'.  */
          int inner;
     
          /* If this call is expanded by the compiler, you may see
             a nested block here whose function is 'inline_function'
             and whose superblock is the one holding 'inner'.  */
          inline_function ();
       }
     }
</pre>
   <p>A <code>gdb.Block</code> is iterable.  The iterator returns the symbols
(see <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>) local to the block.  Python programs
should not assume that a specific block object will always contain a
given symbol, since changes in <span class="sc">gdb</span> features and
infrastructure may cause symbols move across blocks in a symbol
table.

   <p>The following block-related functions are available in the <code>gdb</code>
module:

   <p><a name="index-gdb_002eblock_005ffor_005fpc-2288"></a>

<div class="defun">
&mdash; Function: <b>gdb.block_for_pc</b> (<var>pc</var>)<var><a name="index-gdb_002eblock_005ffor_005fpc-2289"></a></var><br>
<blockquote><p>Return the innermost <code>gdb.Block</code> containing the given <var>pc</var>
value.  If the block cannot be found for the <var>pc</var> value specified,
the function will return <code>None</code>.  This is identical to
<code>gdb.current_progspace().block_for_pc(pc)</code> and is included for
historical compatibility. 
</p></blockquote></div>

   <p>A <code>gdb.Block</code> object has the following methods:

<div class="defun">
&mdash; Function: <b>Block.is_valid</b> ()<var><a name="index-Block_002eis_005fvalid-2290"></a></var><br>
<blockquote><p>Returns <code>True</code> if the <code>gdb.Block</code> object is valid,
<code>False</code> if not.  A block object can become invalid if the block it
refers to doesn't exist anymore in the inferior.  All other
<code>gdb.Block</code> methods will throw an exception if it is invalid at
the time the method is called.  The block's validity is also checked
during iteration over symbols of the block. 
</p></blockquote></div>

   <p>A <code>gdb.Block</code> object has the following attributes:

<div class="defun">
&mdash; Variable: <b>Block.start</b><var><a name="index-Block_002estart-2291"></a></var><br>
<blockquote><p>The start address of the block.  This attribute is not writable. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.end</b><var><a name="index-Block_002eend-2292"></a></var><br>
<blockquote><p>One past the last address that appears in the block.  This attribute
is not writable. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.function</b><var><a name="index-Block_002efunction-2293"></a></var><br>
<blockquote><p>The name of the block represented as a <code>gdb.Symbol</code>.  If the
block is not named, then this attribute holds <code>None</code>.  This
attribute is not writable.

        <p>For ordinary function blocks, the superblock is the static block. 
However, you should note that it is possible for a function block to
have a superblock that is not the static block &ndash; for instance this
happens for an inlined function. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.superblock</b><var><a name="index-Block_002esuperblock-2294"></a></var><br>
<blockquote><p>The block containing this block.  If this parent block does not exist,
this attribute holds <code>None</code>.  This attribute is not writable. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.global_block</b><var><a name="index-Block_002eglobal_005fblock-2295"></a></var><br>
<blockquote><p>The global block associated with this block.  This attribute is not
writable. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.static_block</b><var><a name="index-Block_002estatic_005fblock-2296"></a></var><br>
<blockquote><p>The static block associated with this block.  This attribute is not
writable. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.is_global</b><var><a name="index-Block_002eis_005fglobal-2297"></a></var><br>
<blockquote><p><code>True</code> if the <code>gdb.Block</code> object is a global block,
<code>False</code> if not.  This attribute is not
writable. 
</p></blockquote></div>

<div class="defun">
&mdash; Variable: <b>Block.is_static</b><var><a name="index-Block_002eis_005fstatic-2298"></a></var><br>
<blockquote><p><code>True</code> if the <code>gdb.Block</code> object is a static block,
<code>False</code> if not.  This attribute is not writable. 
</p></blockquote></div>

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