There are a number of language bindings and wrappers available forlibxml2,
the list below is not exhaustive. Please contact the xml-bindings@gnome.org(archives) inorder to
get updates to this list or to discuss the specific topic of libxml2or
libxslt wrappers or bindings: The distribution includes a set of Python bindings, which are guaranteedto
be maintained as part of the library in the future, though the
Pythoninterface have not yet reached the completeness of the C API. Note that some of the Python purist dislike the default set of
Pythonbindings, rather than complaining I suggest they have a look at lxml the more pythonic bindings for
libxml2and libxsltand help
MartijnFaassencomplete those. Stéphane
Bidoulmaintains a
Windows portof the Python bindings. Note to people interested in building bindings, the API is formalized asan XML API description filewhich allows toautomate
a large part of the Python bindings, this includes functiondescriptions,
enums, structures, typedefs, etc... The Python script used tobuild the
bindings is python/generator.py in the source distribution. To install the Python bindings there are 2 options: - If you use an RPM based distribution, simply install the libxml2-pythonRPM(and
if needed the libxslt-pythonRPM).
- Otherwise use the libxml2-pythonmodule
distributioncorresponding to your installed version oflibxml2 and
libxslt. Note that to install it you will need both libxml2and libxslt
installed and run "python setup.py build install" in themodule tree.
The distribution includes a set of examples and regression tests for
thepython bindings in the python/tests directory. Here are
someexcerpts from those tests: tst.py:This is a basic test of the file interface and DOM navigation: import libxml2, sys
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() The Python module is called libxml2; parseFile is the equivalent
ofxmlParseFile (most of the bindings are automatically generated, and the
xmlprefix is removed and the casing convention are kept). All node seen at
thebinding level share the same subset of accessors: name : returns the node name
type : returns a string indicating the node type
content : returns the content of the node, it is based
onxmlNodeGetContent() and hence is recursive.
parent , children ,
last ,next , prev ,
doc ,properties : pointing to the associated
element in the tree,those may return None in case no such link
exists.
Also note the need to explicitly deallocate documents with freeDoc()
.Reference counting for libxml2 trees would need quite a lot of work
tofunction properly, and rather than risk memory leaks if not
implementedcorrectly it sounds safer to have an explicit function to free a
tree. Thewrapper python objects like doc, root or child are them
automatically garbagecollected. validate.py:This test check the validation interfaces and redirection of
errormessages: 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" The first thing to notice is the call to registerErrorHandler(), itdefines
a new error handler global to the library. It is used to avoid seeingthe
error messages when trying to validate the invalid document. The main interest of that test is the creation of a parser context
withcreateFileParserCtxt() and how the behaviour can be changed before
callingparseDocument() . Similarly the informations resulting from the
parsing phaseare also available using context methods. Contexts like nodes are defined as class and the libxml2 wrappers maps
theC function interfaces in terms of objects method as much as possible.
Thebest to get a complete view of what methods are supported is to look at
thelibxml2.py module containing all the wrappers. push.py:This test show how to activate the push parser interface: import libxml2
ctxt = libxml2.createPushParser(None, "<foo", 4, "test.xml")
ctxt.parseChunk("/>", 2, 1)
doc = ctxt.doc()
doc.freeDoc() The context is created with a special call based on
thexmlCreatePushParser() from the C library. The first argument is an
optionalSAX callback object, then the initial set of data, the length and the
name ofthe resource in case URI-References need to be computed by the
parser. Then the data are pushed using the parseChunk() method, the last
callsetting the third argument terminate to 1. pushSAX.py:this test show the use of the event based parsing interfaces. In this
casethe parser does not build a document, but provides callback information
asthe parser makes progresses analyzing the data being provided: 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 The key object in that test is the handler, it provides a number of
entrypoints which can be called by the parser as it makes progresses to
indicatethe information set obtained. The full set of callback is larger than
whatthe callback class in that specific example implements (see the
SAXdefinition for a complete list). The wrapper will only call those supplied
bythe object when activated. The startElement receives the names of the
elementand a dictionary containing the attributes carried by this element. Also note that the reference string generated from the callback shows
asingle character call even though the string "bar" is passed to the
parserfrom 2 different call to parseChunk() xpath.py:This is a basic test of XPath wrappers support 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() This test parses a file, then create an XPath context to evaluate
XPathexpression on it. The xpathEval() method execute an XPath query and
returnsthe 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. Likethe document, the XPath context need to be freed explicitly,
also not thatthe result of the XPath query may point back to the document
tree and hencethe 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
inpython: 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() Note how the extension function is registered with the context (but
thatpart 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
extensionfunction can access the XPath evaluation context: 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 All the interfaces around the XPath parser(or rather evaluation)
contextare not finalized, but it should be sufficient to do contextual work
at theevaluation point. Memory debugging:last but not least, all tests starts with the following prologue: #memory debug specific
libxml2.debugMemory(1) and ends with the following epilogue: #memory debug specific
libxml2.cleanupParser()
if libxml2.debugMemory(1) == 0:
print "OK"
else:
print "Memory leak %d bytes" % (libxml2.debugMemory(1))
libxml2.dumpMemory() Those activate the memory debugging interface of libxml2 where
allallocated block in the library are tracked. The prologue then cleans up
thelibrary state and checks that all allocated memory has been freed. If not
itcalls dumpMemory() which saves that list in a .memdump file. Daniel Veillard |