import sys
from xml.dom.ext.reader import Sax2
from xml import xpath

def file2DOM(filename):
    reader = Sax2.Reader()
    doc = reader.fromStream(filename)
    return doc

def get_from(dom, xpath_expr):
    match = xpath.Evaluate(xpath_expr, dom)
    if match:
        return match[0].nodeValue
    else:
        raise Exception("No %s in the DOM tree" % xpath)

if len(sys.argv) < 3:
    raise Exception("Usage: %s xpath file" % sys.argv[0])
xpath_text = sys.argv[1]
file_dom = file2DOM(sys.argv[2])
print get_from(file_dom, xpath_text)