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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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