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| <h1>The XML C library for Gnome</h1> |
| <h2>Python and bindings</h2> |
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| <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr> |
| <tr><td bgcolor="#fffacd"><ul> |
| <li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li> |
| <li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li> |
| <li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li> |
| <li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li> |
| <li><a href="ftp://xmlsoft.org/">FTP</a></li> |
| <li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li> |
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| <li><a href="http://www.zveno.com/open_source/libxml2xslt.html">MacOsX binaries</a></li> |
| <li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li> |
| <li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml&product=libxml2">Bug Tracker</a></li> |
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| <p>There are a number of language bindings and wrappers available for |
| 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> |
| (<a href="http://mail.gnome.org/archives/xml-bindings/">archives</a>) in |
| order to get updates to this list or to discuss the specific topic of libxml2 |
| or libxslt wrappers or bindings:</p> |
| <ul> |
| <li> |
| <a href="http://libxmlplusplus.sourceforge.net/">Libxml++</a> seems the |
| most up-to-date C++ bindings for libxml2, check the <a href="http://libxmlplusplus.sourceforge.net/reference/html/hierarchy.html">documentation</a> |
| and the <a href="http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/libxmlplusplus/libxml%2b%2b/examples/">examples</a>.</li> |
| <li>There is another <a href="http://libgdome-cpp.berlios.de/">C++ wrapper |
| based on the gdome2 bindings</a> maintained by Tobias Peters.</li> |
| <li>and a third C++ wrapper by Peter Jones <pjones@pmade.org> |
| <p>Website: <a href="http://pmade.org/pjones/software/xmlwrapp/">http://pmade.org/pjones/software/xmlwrapp/</a> |
| </p> |
| </li> |
| <li> |
| <a href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt |
| Sergeant</a> developed <a href="http://axkit.org/download/">XML::LibXSLT</a>, a Perl wrapper for |
| libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML |
| application server</a>.</li> |
| <li> |
| <a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> provides an |
| earlier version of the libxml/libxslt <a href="http://www.rexx.com/~dkuhlman">wrappers for Python</a>.</li> |
| <li>Gopal.V and Peter Minten develop <a href="http://savannah.gnu.org/projects/libxmlsharp">libxml#</a>, a set of |
| C# libxml2 bindings.</li> |
| <li>Petr Kozelka provides <a href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue |
| libxml2</a> with Kylix, Delphi and other Pascal compilers.</li> |
| <li>Uwe Fechner also provides <a href="http://sourceforge.net/projects/idom2-pas/">idom2</a>, a DOM2 |
| implementation for Kylix2/D5/D6 from Borland.</li> |
| <li>Wai-Sun "Squidster" Chia provides <a href="http://www.rubycolor.org/arc/redist/">bindings for Ruby</a> and |
| libxml2 bindings are also available in Ruby through the <a href="http://libgdome-ruby.berlios.de/">libgdome-ruby</a> module |
| maintained by Tobias Peters.</li> |
| <li>Steve Ball and contributors maintains <a href="http://tclxml.sourceforge.net/">libxml2 and libxslt bindings for |
| Tcl</a>.</li> |
| <li>There is support for libxml2 in the DOM module of PHP.</li> |
| </ul> |
| <p>The distribution includes a set of Python bindings, which are guaranteed |
| to be maintained as part of the library in the future, though the Python |
| interface have not yet reached the maturity of the C API.</p> |
| <p>Note to people interested in building bindings, the API is formalized as |
| <a href="libxml2-api.xml">an XML API description file</a> which allows to |
| automate a large part of the Python bindings, this includes function |
| descriptions, enums, structures, typedefs, etc... The Python script used |
| to build the bindings is python/generator.py in the source distribution.</p> |
| <p>To install the Python bindings there are 2 options:</p> |
| <ul> |
| <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 |
| RPM</a> (and if needed the <a href="http://rpmfind.net/linux/rpm2html/search.php?query=libxslt-python">libxslt-python |
| RPM</a>).</li> |
| <li>Otherwise use the <a href="ftp://xmlsoft.org/python/">libxml2-python |
| module distribution</a> corresponding to your installed version of |
| libxml2 and libxslt. Note that to install it you will need both libxml2 |
| and libxslt installed and run "python setup.py build install" in the |
| module tree.</li> |
| </ul> |
| <p>The distribution includes a set of examples and regression tests for the |
| python bindings in the <code>python/tests</code> directory. Here are some |
| excerpts from those tests:</p> |
| <h3>tst.py:</h3> |
| <p>This is a basic test of the file interface and DOM navigation:</p> |
| <pre>import libxml2 |
| |
| doc = libxml2.parseFile("tst.xml") |
| if doc.name != "tst.xml": |
| print "doc.name failed" |
| sys.exit(1) |
| root = doc.children |
| if root.name != "doc": |
| print "root.name failed" |
| sys.exit(1) |
| child = root.children |
| if child.name != "foo": |
| print "child.name failed" |
| sys.exit(1) |
| doc.freeDoc()</pre> |
| <p>The Python module is called libxml2; parseFile is the equivalent of |
| xmlParseFile (most of the bindings are automatically generated, and the xml |
| prefix is removed and the casing convention are kept). All node seen at the |
| binding level share the same subset of accessors:</p> |
| <ul> |
| <li> |
| <code>name</code> : returns the node name</li> |
| <li> |
| <code>type</code> : returns a string indicating the node type</li> |
| <li> |
| <code>content</code> : returns the content of the node, it is based on |
| xmlNodeGetContent() and hence is recursive.</li> |
| <li> |
| <code>parent</code> , <code>children</code>, <code>last</code>, |
| <code>next</code>, <code>prev</code>, <code>doc</code>, |
| <code>properties</code>: pointing to the associated element in the tree, |
| those may return None in case no such link exists.</li> |
| </ul> |
| <p>Also note the need to explicitly deallocate documents with freeDoc() . |
| Reference counting for libxml2 trees would need quite a lot of work to |
| function properly, and rather than risk memory leaks if not implemented |
| correctly it sounds safer to have an explicit function to free a tree. The |
| wrapper python objects like doc, root or child are them automatically garbage |
| collected.</p> |
| <h3>validate.py:</h3> |
| <p>This test check the validation interfaces and redirection of error |
| messages:</p> |
| <pre>import libxml2 |
| |
| #deactivate error messages from the validation |
| def noerr(ctx, str): |
| pass |
| |
| libxml2.registerErrorHandler(noerr, None) |
| |
| ctxt = libxml2.createFileParserCtxt("invalid.xml") |
| ctxt.validate(1) |
| ctxt.parseDocument() |
| doc = ctxt.doc() |
| valid = ctxt.isValid() |
| doc.freeDoc() |
| if valid != 0: |
| print "validity check failed"</pre> |
| <p>The first thing to notice is the call to registerErrorHandler(), it |
| defines a new error handler global to the library. It is used to avoid seeing |
| the error messages when trying to validate the invalid document.</p> |
| <p>The main interest of that test is the creation of a parser context with |
| createFileParserCtxt() and how the behaviour can be changed before calling |
| parseDocument() . Similarly the informations resulting from the parsing phase |
| are also available using context methods.</p> |
| <p>Contexts like nodes are defined as class and the libxml2 wrappers maps the |
| C function interfaces in terms of objects method as much as possible. The |
| best to get a complete view of what methods are supported is to look at the |
| libxml2.py module containing all the wrappers.</p> |
| <h3>push.py:</h3> |
| <p>This test show how to activate the push parser interface:</p> |
| <pre>import libxml2 |
| |
| ctxt = libxml2.createPushParser(None, "<foo", 4, "test.xml") |
| ctxt.parseChunk("/>", 2, 1) |
| doc = ctxt.doc() |
| |
| doc.freeDoc()</pre> |
| <p>The context is created with a special call based on the |
| xmlCreatePushParser() from the C library. The first argument is an optional |
| SAX callback object, then the initial set of data, the length and the name of |
| the resource in case URI-References need to be computed by the parser.</p> |
| <p>Then the data are pushed using the parseChunk() method, the last call |
| setting the third argument terminate to 1.</p> |
| <h3>pushSAX.py:</h3> |
| <p>this test show the use of the event based parsing interfaces. In this case |
| the parser does not build a document, but provides callback information as |
| the parser makes progresses analyzing the data being provided:</p> |
| <pre>import libxml2 |
| log = "" |
| |
| class callback: |
| def startDocument(self): |
| global log |
| log = log + "startDocument:" |
| |
| def endDocument(self): |
| global log |
| log = log + "endDocument:" |
| |
| def startElement(self, tag, attrs): |
| global log |
| log = log + "startElement %s %s:" % (tag, attrs) |
| |
| def endElement(self, tag): |
| global log |
| log = log + "endElement %s:" % (tag) |
| |
| def characters(self, data): |
| global log |
| log = log + "characters: %s:" % (data) |
| |
| def warning(self, msg): |
| global log |
| log = log + "warning: %s:" % (msg) |
| |
| def error(self, msg): |
| global log |
| log = log + "error: %s:" % (msg) |
| |
| def fatalError(self, msg): |
| global log |
| log = log + "fatalError: %s:" % (msg) |
| |
| handler = callback() |
| |
| ctxt = libxml2.createPushParser(handler, "<foo", 4, "test.xml") |
| chunk = " url='tst'>b" |
| ctxt.parseChunk(chunk, len(chunk), 0) |
| chunk = "ar</foo>" |
| ctxt.parseChunk(chunk, len(chunk), 1) |
| |
| reference = "startDocument:startElement foo {'url': 'tst'}:" + \ |
| "characters: bar:endElement foo:endDocument:" |
| if log != reference: |
| print "Error got: %s" % log |
| print "Expected: %s" % reference</pre> |
| <p>The key object in that test is the handler, it provides a number of entry |
| points which can be called by the parser as it makes progresses to indicate |
| the information set obtained. The full set of callback is larger than what |
| the callback class in that specific example implements (see the SAX |
| definition for a complete list). The wrapper will only call those supplied by |
| the object when activated. The startElement receives the names of the element |
| and a dictionary containing the attributes carried by this element.</p> |
| <p>Also note that the reference string generated from the callback shows a |
| single character call even though the string "bar" is passed to the parser |
| from 2 different call to parseChunk()</p> |
| <h3>xpath.py:</h3> |
| <p>This is a basic test of XPath wrappers support</p> |
| <pre>import libxml2 |
| |
| doc = libxml2.parseFile("tst.xml") |
| ctxt = doc.xpathNewContext() |
| res = ctxt.xpathEval("//*") |
| if len(res) != 2: |
| print "xpath query: wrong node set size" |
| sys.exit(1) |
| if res[0].name != "doc" or res[1].name != "foo": |
| print "xpath query: wrong node set value" |
| sys.exit(1) |
| doc.freeDoc() |
| ctxt.xpathFreeContext()</pre> |
| <p>This test parses a file, then create an XPath context to evaluate XPath |
| expression on it. The xpathEval() method execute an XPath query and returns |
| the result mapped in a Python way. String and numbers are natively converted, |
| and node sets are returned as a tuple of libxml2 Python nodes wrappers. Like |
| the document, the XPath context need to be freed explicitly, also not that |
| the result of the XPath query may point back to the document tree and hence |
| the document must be freed after the result of the query is used.</p> |
| <h3>xpathext.py:</h3> |
| <p>This test shows how to extend the XPath engine with functions written in |
| python:</p> |
| <pre>import libxml2 |
| |
| def foo(ctx, x): |
| return x + 1 |
| |
| doc = libxml2.parseFile("tst.xml") |
| ctxt = doc.xpathNewContext() |
| libxml2.registerXPathFunction(ctxt._o, "foo", None, foo) |
| res = ctxt.xpathEval("foo(1)") |
| if res != 2: |
| print "xpath extension failure" |
| doc.freeDoc() |
| ctxt.xpathFreeContext()</pre> |
| <p>Note how the extension function is registered with the context (but that |
| part is not yet finalized, this may change slightly in the future).</p> |
| <h3>tstxpath.py:</h3> |
| <p>This test is similar to the previous one but shows how the extension |
| function can access the XPath evaluation context:</p> |
| <pre>def foo(ctx, x): |
| global called |
| |
| # |
| # test that access to the XPath evaluation contexts |
| # |
| pctxt = libxml2.xpathParserContext(_obj=ctx) |
| ctxt = pctxt.context() |
| called = ctxt.function() |
| return x + 1</pre> |
| <p>All the interfaces around the XPath parser(or rather evaluation) context |
| are not finalized, but it should be sufficient to do contextual work at the |
| evaluation point.</p> |
| <h3>Memory debugging:</h3> |
| <p>last but not least, all tests starts with the following prologue:</p> |
| <pre>#memory debug specific |
| libxml2.debugMemory(1)</pre> |
| <p>and ends with the following epilogue:</p> |
| <pre>#memory debug specific |
| libxml2.cleanupParser() |
| if libxml2.debugMemory(1) == 0: |
| print "OK" |
| else: |
| print "Memory leak %d bytes" % (libxml2.debugMemory(1)) |
| libxml2.dumpMemory()</pre> |
| <p>Those activate the memory debugging interface of libxml2 where all |
| allocated block in the library are tracked. The prologue then cleans up the |
| library state and checks that all allocated memory has been freed. If not it |
| calls dumpMemory() which saves that list in a <code>.memdump</code> file.</p> |
| <p><a href="bugs.html">Daniel Veillard</a></p> |
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