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</style><title>Python and bindings</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"> | | The XML C parser and toolkit of GnomePython and bindings |
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<center>Developer Menu</center> | <form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form> |
<center>API Indexes</center> | |
<center>Related links</center> | |
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| 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 xml-bindings@gnome.org
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(archives) 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:
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Libxml++ seems the
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most up-to-date C++ bindings for libxml2, check the documentation
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and the examples.
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There is another C++ wrapper
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based on the gdome2 bindings maintained by Tobias Peters.
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and a third C++ wrapper by Peter Jones <pjones@pmade.org>
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Website: http://pmade.org/pjones/software/xmlwrapp/
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XML::LibXML Perl
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bindings are available on CPAN, as well as XML::LibXSLT
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Perl libxslt
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bindings.
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If you're interested into scripting XML processing, have a look at XSH an XML editing shell based on
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Libxml2 Perl bindings.
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Dave Kuhlman provides an
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earlier version of the libxml/libxslt wrappers for Python.
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Gopal.V and Peter Minten develop libxml#, a set of
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C# libxml2 bindings.
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Petr Kozelka provides Pascal units to glue
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libxml2 with Kylix, Delphi and other Pascal compilers.
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Uwe Fechner also provides idom2, a DOM2
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implementation for Kylix2/D5/D6 from Borland.
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There is bindings for Ruby
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and libxml2 bindings are also available in Ruby through the libgdome-ruby module
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maintained by Tobias Peters.
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Steve Ball and contributors maintains libxml2 and libxslt bindings for
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Tcl.
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libxml2 and libxslt are the default XML libraries for PHP5.
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LibxmlJ is
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an effort to create a 100% JAXP-compatible Java wrapper for libxml2 and
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libxslt as part of GNU ClasspathX project.
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Patrick McPhee provides Rexx bindings fof libxml2 and libxslt, look for
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RexxXML.
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Satimage
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provides XMLLib
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osax. This is an osax for Mac OS X with a set of commands to
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implement in AppleScript the XML DOM, XPATH and XSLT. Also includes
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commands for Property-lists (Apple's fast lookup table XML format.)
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Francesco Montorsi developped wxXml2
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wrappers that interface libxml2, allowing wxWidgets applications to
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load/save/edit XML instances.
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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 completeness of the C API.Note that some of the Python purist dislike the default set of Python
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bindings, rather than complaining I suggest they have a look at lxml the more pythonic bindings for libxml2
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and libxslt and check the mailing-list.Stéphane Bidoul
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maintains a Windows port
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of the Python bindings.Note to people interested in building bindings, the API is formalized as
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an XML API description file which allows to
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automate a large part of the Python bindings, this includes function
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descriptions, enums, structures, typedefs, etc... The Python script used to
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build the bindings is python/generator.py in the source distribution.To install the Python bindings there are 2 options:
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If you use an RPM based distribution, simply install the libxml2-python
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RPM (and if needed the libxslt-python
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RPM).
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Otherwise use the libxml2-python
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module distribution 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.
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The distribution includes a set of examples and regression tests for the
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python bindings in the python/tests directory. Here are some
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excerpts from those tests:tst.py:This is a basic test of the file interface and DOM navigation: import libxml2, sys
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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()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:
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name : returns the node name
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type : returns a string indicating the node type
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content : returns the content of the node, it is based on
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xmlNodeGetContent() and hence is recursive.
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parent , children , last ,
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next , prev , doc ,
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properties : pointing to the associated element in the tree,
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those may return None in case no such link exists.
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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.validate.py:This test check the validation interfaces and redirection of error
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messages: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"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.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 information resulting from the parsing phase
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is also available using context methods.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.push.py:This test show how to activate the push parser interface: 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()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.Then the data are pushed using the parseChunk() method, the last call
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setting the third argument terminate to 1.pushSAX.py: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: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" % referenceThe 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.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()xpath.py:This is a basic test of XPath wrappers support 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()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.xpathext.py:This test shows how to extend the XPath engine with functions written in
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python: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()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).tstxpath.py:This test is similar to the previous one but shows how the extension
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function can access the XPath evaluation context: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 + 1All 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.Memory debugging:last but not least, all tests starts with the following prologue: #memory debug specific
|
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libxml2.debugMemory(1)and ends with the following epilogue: #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()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 .memdump file.Daniel Veillard </body></html>
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