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378 lines
18 KiB
HTML
378 lines
18 KiB
HTML
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<title>Python and bindings</title>
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<body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000">
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<table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr>
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<td width="180">
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<a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo"></a></div>
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</td>
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<td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center">
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<h1>The XML C library for Gnome</h1>
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<h2>Python and bindings</h2>
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</td></tr></table></td></tr></table></td>
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</tr></table>
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<table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="index.html">Home</a></li>
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<li><a href="intro.html">Introduction</a></li>
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<li><a href="FAQ.html">FAQ</a></li>
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<li><a href="docs.html">Documentation</a></li>
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<li><a href="bugs.html">Reporting bugs and getting help</a></li>
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<li><a href="help.html">How to help</a></li>
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<li><a href="downloads.html">Downloads</a></li>
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<li><a href="news.html">News</a></li>
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<li><a href="XMLinfo.html">XML</a></li>
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<li><a href="XSLT.html">XSLT</a></li>
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<li><a href="python.html">Python and bindings</a></li>
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<li><a href="architecture.html">libxml architecture</a></li>
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<li><a href="tree.html">The tree output</a></li>
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<li><a href="interface.html">The SAX interface</a></li>
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<li><a href="xmldtd.html">Validation & DTDs</a></li>
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<li><a href="xmlmem.html">Memory Management</a></li>
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<li><a href="encoding.html">Encodings support</a></li>
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<li><a href="xmlio.html">I/O Interfaces</a></li>
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<li><a href="catalog.html">Catalog support</a></li>
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<li><a href="library.html">The parser interfaces</a></li>
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<li><a href="entities.html">Entities or no entities</a></li>
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<li><a href="namespaces.html">Namespaces</a></li>
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<li><a href="upgrade.html">Upgrading 1.x code</a></li>
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<li><a href="threads.html">Thread safety</a></li>
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<li><a href="DOM.html">DOM Principles</a></li>
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<li><a href="example.html">A real example</a></li>
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<li><a href="contribs.html">Contributions</a></li>
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<li><a href="tutorial/index.html">Tutorial</a></li>
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<li>
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<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a>
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</li>
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</ul></td></tr>
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</table>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr>
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<tr><td bgcolor="#fffacd">
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<form action="search.php" enctype="application/x-www-form-urlencoded" method="GET">
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<input name="query" type="TEXT" size="20" value=""><input name="submit" type="submit" value="Search ...">
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</form>
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<ul>
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<li><a href="APIchunk0.html">Alphabetic</a></li>
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<li><a href="APIconstructors.html">Constructors</a></li>
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<li><a href="APIfunctions.html">Functions/Types</a></li>
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<li><a href="APIfiles.html">Modules</a></li>
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<li><a href="APIsymbols.html">Symbols</a></li>
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</ul>
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</td></tr>
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</table>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
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<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
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<li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li>
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<li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li>
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<li><a href="ftp://xmlsoft.org/">FTP</a></li>
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<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li>
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<li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li>
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<li><a href="http://www.zveno.com/open_source/libxml2xslt.html">MacOsX binaries</a></li>
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<li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li>
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<li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml&product=libxml2">Bug Tracker</a></li>
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</ul></td></tr>
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</table>
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</td></tr></table></td>
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<td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd">
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<p>There are a number of language bindings and wrappers available for
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libxml2, the list below is not exhaustive. Please contact the <a href="http://mail.gnome.org/mailman/listinfo/xml-bindings">xml-bindings@gnome.org</a>
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(<a href="http://mail.gnome.org/archives/xml-bindings/">archives</a>) in
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order to get updates to this list or to discuss the specific topic of libxml2
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or libxslt wrappers or bindings:</p>
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<ul>
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<li>
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<a href="mailto:ari@lusis.org">Ari Johnson</a> provides a C++ wrapper
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for libxml:<br>
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Website: <a href="http://lusis.org/~ari/xml%2B%2B/">http://lusis.org/~ari/xml++/</a><br>
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Download: <a href="http://lusis.org/~ari/xml%2B%2B/libxml%2B%2B.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a>
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</li>
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<li>There is another <a href="http://libgdome-cpp.berlios.de/">C++ wrapper
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based on the gdome2 bindings</a> maintained by Tobias Peters.</li>
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<li>and a third C++ wrapper by Peter Jones <pjones@pmade.org>
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<p>Website: <a href="http://pmade.org/pjones/software/xmlwrapp/">http://pmade.org/pjones/software/xmlwrapp/</a>
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</p>
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</li>
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<li>
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<a href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt
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Sergeant</a> developed <a href="http://axkit.org/download/">XML::LibXSLT</a>, a Perl wrapper for
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libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML
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application server</a>.</li>
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<li>
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<a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> provides an
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earlier version of the libxml/libxslt <a href="http://www.rexx.com/~dkuhlman">wrappers for Python</a>.</li>
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<li>Gopal.V and Peter Minten develop <a href="http://savannah.gnu.org/projects/libxmlsharp">libxml#</a>, a set of
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C# libxml2 bindings.</li>
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<li>Petr Kozelka provides <a href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue
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libxml2</a> with Kylix, Delphi and other Pascal compilers.</li>
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<li>Uwe Fechner also provides <a href="http://sourceforge.net/projects/idom2-pas/">idom2</a>, a DOM2
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implementation for Kylix2/D5/D6 from Borland.</li>
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<li>Wai-Sun "Squidster" Chia provides <a href="http://www.rubycolor.org/arc/redist/">bindings for Ruby</a> and
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libxml2 bindings are also available in Ruby through the <a href="http://libgdome-ruby.berlios.de/">libgdome-ruby</a> module
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maintained by Tobias Peters.</li>
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<li>Steve Ball and contributors maintains <a href="http://tclxml.sourceforge.net/">libxml2 and libxslt bindings for
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Tcl</a>.</li>
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<li>There is support for libxml2 in the DOM module of PHP.</li>
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</ul>
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<p>The distribution includes a set of Python bindings, which are guaranteed
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to be maintained as part of the library in the future, though the Python
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interface have not yet reached the maturity of the C API.</p>
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<p>To install the Python bindings there are 2 options:</p>
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<ul>
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<li>If you use an RPM based distribution, simply install the <a href="http://rpmfind.net/linux/rpm2html/search.php?query=libxml2-python">libxml2-python
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RPM</a> (and if needed the <a href="http://rpmfind.net/linux/rpm2html/search.php?query=libxslt-python">libxslt-python
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RPM</a>).</li>
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<li>Otherwise use the <a href="ftp://xmlsoft.org/python/">libxml2-python
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module distribution</a> corresponding to your installed version of
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libxml2 and libxslt. Note that to install it you will need both libxml2
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and libxslt installed and run "python setup.py build install" in the
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module tree.</li>
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</ul>
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<p>The distribution includes a set of examples and regression tests for the
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python bindings in the <code>python/tests</code> directory. Here are some
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excerpts from those tests:</p>
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<h3>tst.py:</h3>
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<p>This is a basic test of the file interface and DOM navigation:</p>
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<pre>import libxml2
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doc = libxml2.parseFile("tst.xml")
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if doc.name != "tst.xml":
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print "doc.name failed"
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sys.exit(1)
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root = doc.children
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if root.name != "doc":
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print "root.name failed"
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sys.exit(1)
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child = root.children
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if child.name != "foo":
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print "child.name failed"
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sys.exit(1)
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doc.freeDoc()</pre>
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<p>The Python module is called libxml2; parseFile is the equivalent of
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xmlParseFile (most of the bindings are automatically generated, and the xml
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prefix is removed and the casing convention are kept). All node seen at the
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binding level share the same subset of accessors:</p>
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<ul>
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<li>
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<code>name</code> : returns the node name</li>
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<li>
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<code>type</code> : returns a string indicating the node type</li>
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<li>
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<code>content</code> : returns the content of the node, it is based on
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xmlNodeGetContent() and hence is recursive.</li>
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<li>
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<code>parent</code> , <code>children</code>, <code>last</code>,
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<code>next</code>, <code>prev</code>, <code>doc</code>,
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<code>properties</code>: pointing to the associated element in the tree,
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those may return None in case no such link exists.</li>
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</ul>
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<p>Also note the need to explicitly deallocate documents with freeDoc() .
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Reference counting for libxml2 trees would need quite a lot of work to
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function properly, and rather than risk memory leaks if not implemented
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correctly it sounds safer to have an explicit function to free a tree. The
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wrapper python objects like doc, root or child are them automatically garbage
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collected.</p>
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<h3>validate.py:</h3>
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<p>This test check the validation interfaces and redirection of error
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messages:</p>
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<pre>import libxml2
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#deactivate error messages from the validation
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def noerr(ctx, str):
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pass
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libxml2.registerErrorHandler(noerr, None)
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ctxt = libxml2.createFileParserCtxt("invalid.xml")
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ctxt.validate(1)
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ctxt.parseDocument()
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doc = ctxt.doc()
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valid = ctxt.isValid()
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doc.freeDoc()
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if valid != 0:
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print "validity check failed"</pre>
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<p>The first thing to notice is the call to registerErrorHandler(), it
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defines a new error handler global to the library. It is used to avoid seeing
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the error messages when trying to validate the invalid document.</p>
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<p>The main interest of that test is the creation of a parser context with
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createFileParserCtxt() and how the behaviour can be changed before calling
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parseDocument() . Similarly the informations resulting from the parsing phase
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are also available using context methods.</p>
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<p>Contexts like nodes are defined as class and the libxml2 wrappers maps the
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C function interfaces in terms of objects method as much as possible. The
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best to get a complete view of what methods are supported is to look at the
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libxml2.py module containing all the wrappers.</p>
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<h3>push.py:</h3>
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<p>This test show how to activate the push parser interface:</p>
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<pre>import libxml2
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ctxt = libxml2.createPushParser(None, "<foo", 4, "test.xml")
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ctxt.parseChunk("/>", 2, 1)
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doc = ctxt.doc()
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doc.freeDoc()</pre>
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<p>The context is created with a special call based on the
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xmlCreatePushParser() from the C library. The first argument is an optional
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SAX callback object, then the initial set of data, the length and the name of
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the resource in case URI-References need to be computed by the parser.</p>
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<p>Then the data are pushed using the parseChunk() method, the last call
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setting the third argument terminate to 1.</p>
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<h3>pushSAX.py:</h3>
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<p>this test show the use of the event based parsing interfaces. In this case
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the parser does not build a document, but provides callback information as
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the parser makes progresses analyzing the data being provided:</p>
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<pre>import libxml2
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log = ""
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class callback:
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def startDocument(self):
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global log
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log = log + "startDocument:"
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def endDocument(self):
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global log
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log = log + "endDocument:"
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def startElement(self, tag, attrs):
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global log
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log = log + "startElement %s %s:" % (tag, attrs)
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def endElement(self, tag):
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global log
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log = log + "endElement %s:" % (tag)
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def characters(self, data):
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global log
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log = log + "characters: %s:" % (data)
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def warning(self, msg):
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global log
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log = log + "warning: %s:" % (msg)
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def error(self, msg):
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global log
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log = log + "error: %s:" % (msg)
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def fatalError(self, msg):
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global log
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log = log + "fatalError: %s:" % (msg)
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handler = callback()
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ctxt = libxml2.createPushParser(handler, "<foo", 4, "test.xml")
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chunk = " url='tst'>b"
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ctxt.parseChunk(chunk, len(chunk), 0)
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chunk = "ar</foo>"
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ctxt.parseChunk(chunk, len(chunk), 1)
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reference = "startDocument:startElement foo {'url': 'tst'}:" + \
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"characters: bar:endElement foo:endDocument:"
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if log != reference:
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print "Error got: %s" % log
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print "Expected: %s" % reference</pre>
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<p>The key object in that test is the handler, it provides a number of entry
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points which can be called by the parser as it makes progresses to indicate
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the information set obtained. The full set of callback is larger than what
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the callback class in that specific example implements (see the SAX
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definition for a complete list). The wrapper will only call those supplied by
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the object when activated. The startElement receives the names of the element
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and a dictionary containing the attributes carried by this element.</p>
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<p>Also note that the reference string generated from the callback shows a
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single character call even though the string "bar" is passed to the parser
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from 2 different call to parseChunk()</p>
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<h3>xpath.py:</h3>
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<p>This is a basic test of XPath wrappers support</p>
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<pre>import libxml2
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doc = libxml2.parseFile("tst.xml")
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ctxt = doc.xpathNewContext()
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res = ctxt.xpathEval("//*")
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if len(res) != 2:
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print "xpath query: wrong node set size"
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sys.exit(1)
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if res[0].name != "doc" or res[1].name != "foo":
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print "xpath query: wrong node set value"
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sys.exit(1)
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doc.freeDoc()
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ctxt.xpathFreeContext()</pre>
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<p>This test parses a file, then create an XPath context to evaluate XPath
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expression on it. The xpathEval() method execute an XPath query and returns
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the result mapped in a Python way. String and numbers are natively converted,
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and node sets are returned as a tuple of libxml2 Python nodes wrappers. Like
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the document, the XPath context need to be freed explicitly, also not that
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the result of the XPath query may point back to the document tree and hence
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the document must be freed after the result of the query is used.</p>
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<h3>xpathext.py:</h3>
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<p>This test shows how to extend the XPath engine with functions written in
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python:</p>
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<pre>import libxml2
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def foo(ctx, x):
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return x + 1
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doc = libxml2.parseFile("tst.xml")
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ctxt = doc.xpathNewContext()
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libxml2.registerXPathFunction(ctxt._o, "foo", None, foo)
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res = ctxt.xpathEval("foo(1)")
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if res != 2:
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print "xpath extension failure"
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doc.freeDoc()
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ctxt.xpathFreeContext()</pre>
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<p>Note how the extension function is registered with the context (but that
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part is not yet finalized, this may change slightly in the future).</p>
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<h3>tstxpath.py:</h3>
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<p>This test is similar to the previous one but shows how the extension
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function can access the XPath evaluation context:</p>
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<pre>def foo(ctx, x):
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global called
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#
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# test that access to the XPath evaluation contexts
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#
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pctxt = libxml2.xpathParserContext(_obj=ctx)
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ctxt = pctxt.context()
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called = ctxt.function()
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return x + 1</pre>
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<p>All the interfaces around the XPath parser(or rather evaluation) context
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are not finalized, but it should be sufficient to do contextual work at the
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evaluation point.</p>
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<h3>Memory debugging:</h3>
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<p>last but not least, all tests starts with the following prologue:</p>
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<pre>#memory debug specific
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libxml2.debugMemory(1)</pre>
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<p>and ends with the following epilogue:</p>
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<pre>#memory debug specific
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libxml2.cleanupParser()
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if libxml2.debugMemory(1) == 0:
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print "OK"
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else:
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print "Memory leak %d bytes" % (libxml2.debugMemory(1))
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libxml2.dumpMemory()</pre>
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<p>Those activate the memory debugging interface of libxml2 where all
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allocated block in the library are tracked. The prologue then cleans up the
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library state and checks that all allocated memory has been freed. If not it
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calls dumpMemory() which saves that list in a <code>.memdump</code> file.</p>
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<p><a href="bugs.html">Daniel Veillard</a></p>
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</td></tr></table></td></tr></table></td></tr></table></td>
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</tr></table></td></tr></table>
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</body>
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