python.pdf

and libxslt installed and run "python setup.py build install" in the
module tree.
The distribution includes a set of examples and regression tests for the
python bindings in the python/tests directory. Here are some
excerpts from those tests:tst.py:This is a basic test of the file interface an
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 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:name : returns the n
type : returns a string indicating the node type
content : returns the content of the node, it is based on
xmlNodeGetContent() 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 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.validate.py:This test check the validation interfaces and redirectio
messages: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 registerErr
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.The main interest of th
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.Contexts like nodes are defined as class and t
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.push.py:This test show how to ac

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 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.Then the data are
setting the third argument terminate to 1.pushSAX.py:this test show the use of
the parser does not build a document, but provides callback information as
the 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" % referenceThe key object in that test is the handler, it pr
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.Also note that the r
single character call even though the string "bar" is passed to the parser
from 2 different call to parseChunk()xpath.py:This is a basic test of XPath wr
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 evalu
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.xpathext.py:T
python: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
part is not yet finalized, this may change slightly in the future).tstxpath.py:

calls dumpMemory() which saves that list in a .memdump file.