import xml.dom.minidom
import os, sys

global nest
nest = 0

def trace(frame, event, arg):
    global nest
    
    print "%s%s %s %d" % (
        "   " * nest,
        event,
        os.path.basename(frame.f_code.co_filename),
        frame.f_lineno
        )
    
    if event == 'call':
        nest += 1
    if event == 'return':
        nest -= 1
        
    return trace

sys.settrace(trace)

XML = '''\
<!DOCTYPE fooey SYSTEM "http://www.example.com/example.dtd">
<root><child/><child/></root>
'''

def foo():
    dom = xml.dom.minidom.parseString(XML)
    assert len(dom.getElementsByTagName('child')) == 2
    print "Parsed"

foo()