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223 lines
9.4 KiB
HTML
223 lines
9.4 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Blocks In Python (Debugging with GDB)</title>
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<meta name="description" content="Blocks In Python (Debugging with GDB)">
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<meta name="keywords" content="Blocks In Python (Debugging with GDB)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Python-API.html#Python-API" rel="up" title="Python API">
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<link href="Symbols-In-Python.html#Symbols-In-Python" rel="next" title="Symbols In Python">
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<link href="Frames-In-Python.html#Frames-In-Python" rel="prev" title="Frames In Python">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Blocks-In-Python"></a>
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<div class="header">
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<p>
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Next: <a href="Symbols-In-Python.html#Symbols-In-Python" accesskey="n" rel="next">Symbols In Python</a>, Previous: <a href="Frames-In-Python.html#Frames-In-Python" accesskey="p" rel="prev">Frames 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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</div>
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<hr>
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<a name="Accessing-blocks-from-Python"></a>
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<h4 class="subsubsection">23.2.2.26 Accessing blocks from Python</h4>
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<a name="index-blocks-in-python"></a>
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<a name="index-gdb_002eBlock"></a>
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<p>In <small>GDB</small>, symbols are stored in blocks. A block corresponds
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roughly to a scope in the source code. Blocks are organized
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hierarchically, and are represented individually in Python as a
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<code>gdb.Block</code>. Blocks rely on debugging information being
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available.
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</p>
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<p>A frame has a block. Please see <a href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>, for a more
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in-depth discussion of frames.
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</p>
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<p>The outermost block is known as the <em>global block</em>. The global
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block typically holds public global variables and functions.
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</p>
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<p>The block nested just inside the global block is the <em>static
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block</em>. The static block typically holds file-scoped variables and
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functions.
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</p>
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<p><small>GDB</small> provides a method to get a block’s superblock, but there
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is currently no way to examine the sub-blocks of a block, or to
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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>).
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</p>
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<p>Here is a short example that should help explain blocks:
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</p>
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<div class="smallexample">
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<pre class="smallexample">/* This is in the global block. */
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int global;
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/* This is in the static block. */
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static int file_scope;
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/* 'function' is in the global block, and 'argument' is
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in a block nested inside of 'function'. */
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int function (int argument)
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{
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/* 'local' is in a block inside 'function'. It may or may
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not be in the same block as 'argument'. */
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int local;
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{
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/* 'inner' is in a block whose superblock is the one holding
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'local'. */
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int inner;
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/* If this call is expanded by the compiler, you may see
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a nested block here whose function is 'inline_function'
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and whose superblock is the one holding 'inner'. */
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inline_function ();
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}
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}
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</pre></div>
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<p>A <code>gdb.Block</code> is iterable. The iterator returns the symbols
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(see <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>) local to the block. Python programs
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should not assume that a specific block object will always contain a
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given symbol, since changes in <small>GDB</small> features and
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infrastructure may cause symbols move across blocks in a symbol
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table.
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</p>
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<p>The following block-related functions are available in the <code>gdb</code>
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module:
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</p>
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<a name="index-gdb_002eblock_005ffor_005fpc"></a>
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<dl>
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<dt><a name="index-gdb_002eblock_005ffor_005fpc-1"></a>Function: <strong>gdb.block_for_pc</strong> <em>(pc)</em></dt>
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<dd><p>Return the innermost <code>gdb.Block</code> containing the given <var>pc</var>
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value. If the block cannot be found for the <var>pc</var> value specified,
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the function will return <code>None</code>. This is identical to
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<code>gdb.current_progspace().block_for_pc(pc)</code> and is included for
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historical compatibility.
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</p></dd></dl>
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<p>A <code>gdb.Block</code> object has the following methods:
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</p>
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<dl>
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<dt><a name="index-Block_002eis_005fvalid"></a>Function: <strong>Block.is_valid</strong> <em>()</em></dt>
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<dd><p>Returns <code>True</code> if the <code>gdb.Block</code> object is valid,
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<code>False</code> if not. A block object can become invalid if the block it
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refers to doesn’t exist anymore in the inferior. All other
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<code>gdb.Block</code> methods will throw an exception if it is invalid at
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the time the method is called. The block’s validity is also checked
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during iteration over symbols of the block.
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</p></dd></dl>
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<p>A <code>gdb.Block</code> object has the following attributes:
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</p>
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<dl>
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<dt><a name="index-Block_002estart"></a>Variable: <strong>Block.start</strong></dt>
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<dd><p>The start address of the block. This attribute is not writable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002eend"></a>Variable: <strong>Block.end</strong></dt>
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<dd><p>One past the last address that appears in the block. This attribute
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is not writable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002efunction"></a>Variable: <strong>Block.function</strong></dt>
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<dd><p>The name of the block represented as a <code>gdb.Symbol</code>. If the
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block is not named, then this attribute holds <code>None</code>. This
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attribute is not writable.
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</p>
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<p>For ordinary function blocks, the superblock is the static block.
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However, you should note that it is possible for a function block to
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have a superblock that is not the static block – for instance this
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happens for an inlined function.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002esuperblock"></a>Variable: <strong>Block.superblock</strong></dt>
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<dd><p>The block containing this block. If this parent block does not exist,
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this attribute holds <code>None</code>. This attribute is not writable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002eglobal_005fblock"></a>Variable: <strong>Block.global_block</strong></dt>
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<dd><p>The global block associated with this block. This attribute is not
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writable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002estatic_005fblock"></a>Variable: <strong>Block.static_block</strong></dt>
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<dd><p>The static block associated with this block. This attribute is not
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writable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002eis_005fglobal"></a>Variable: <strong>Block.is_global</strong></dt>
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<dd><p><code>True</code> if the <code>gdb.Block</code> object is a global block,
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<code>False</code> if not. This attribute is not
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writable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Block_002eis_005fstatic"></a>Variable: <strong>Block.is_static</strong></dt>
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<dd><p><code>True</code> if the <code>gdb.Block</code> object is a static block,
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<code>False</code> if not. This attribute is not writable.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Symbols-In-Python.html#Symbols-In-Python" accesskey="n" rel="next">Symbols In Python</a>, Previous: <a href="Frames-In-Python.html#Frames-In-Python" accesskey="p" rel="prev">Frames 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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</div>
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