Parsing XML Entity with python xml.sax

Question

Parsing XML with python using xml.sax, but my code fails to catch Entities. Why doesn\'t skippedEntity() or resolveEntity() report in the following:

import          


        

Answer 1

Here is a modified version of your program that I hope makes sense. It demonstrates a case where all TestHandler methods are called.

import StringIO
import xml.sax
from xml.sax.handler import ContentHandler

# Inheriting from EntityResolver and DTDHandler is not necessary
class TestHandler(ContentHandler):

    # This method is only called for external entities. Must return a value. 
    def resolveEntity(self, publicID, systemID):
        print "TestHandler.resolveEntity(): %s %s" % (publicID, systemID)
        return systemID

    def skippedEntity(self, name):
        print "TestHandler.skippedEntity(): %s" % (name)

    def unparsedEntityDecl(self, name, publicID, systemID, ndata):
        print "TestHandler.unparsedEntityDecl(): %s %s" % (publicID, systemID)

    def startElement(self, name, attrs):
        summary = attrs.get('summary', '')
        print 'TestHandler.startElement():', summary

def main(xml_string):
    try:
        parser = xml.sax.make_parser()
        curHandler = TestHandler()
        parser.setContentHandler(curHandler)
        parser.setEntityResolver(curHandler)
        parser.setDTDHandler(curHandler)

        stream = StringIO.StringIO(xml_string)
        parser.parse(stream)
        stream.close()
    except xml.sax.SAXParseException, e:
        print "*** PARSER error: %s" % e

XML = """<!DOCTYPE test SYSTEM "test.dtd">
<test summary='step: &num;'>Entity: &not;</test>
"""

main(XML)

test.dtd contains:

<!ENTITY num "FOO">
<!ENTITY pic SYSTEM 'bar.gif' NDATA gif>

Output:

TestHandler.resolveEntity(): None test.dtd
TestHandler.unparsedEntityDecl(): None bar.gif
TestHandler.startElement(): step: FOO
TestHandler.skippedEntity(): not

Addition

As far as I can tell, skippedEntity is called only when an external DTD is used (at least I can't come up with a counterexample; it would be nice if the the documentation was a little clearer).

Adam said in his answer that resolveEntity is called only for external DTDs. But that is not quite true. resolveEntity is also called when processing a reference to an external entity that is declared in an internal or external DTD subset. For example:

<!DOCTYPE test [
<!ENTITY num SYSTEM "bar.txt">
]>

where the content of bar.txt could be, say, FOO. In this case it is not possible to refer to the entity in an attribute value.

Answer 2

I think resolveEntity and skippedEntity are only called for external DTDs. I got this to work by modifying the XML.

XML = """<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE test SYSTEM "external.dtd" >
<test summary='step: &foo; &bar;'>Entity: &not;</test>
"""

The external.dtd contains two simple entity declarations.

<!ENTITY foo "bar">
<!ENTITY bar "foo">

Also, I got rid of resolveEntity.

This outputs -

TestHandler.startElement(), test : step: bar foo ()
TestHandler.skippedEntity: not

Hope this helps.