<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_xml(html, content_tag='ekb', fail_if_empty=False):
 """Extract the content XML from the HTML output of the TRIPS web service. Parameters html : str The HTML output from the TRIPS web service. content_tag : str The xml tag used to label the content. Default is 'ekb'. fail_if_empty : bool If True, and if the xml content found is an empty string, raise an exception. Default is False. Returns ------- The extraction knowledge base (e.g. EKB) XML that contains the event and term extractions. """

    cont = re.findall(r'<%(tag)s(.*?)>(.*?)</%(tag)s>' % {'tag': content_tag},
                      html, re.MULTILINE | re.DOTALL)
    if cont:
        events_terms = ''.join([l.strip() for l in cont[0][1].splitlines()])
        if 'xmlns' in cont[0][0]:
            meta = ' '.join([l.strip() for l in cont[0][0].splitlines()])
        else:
            meta = ''
    else:
        events_terms = ''
        meta = ''

    if fail_if_empty:
        assert events_terms != '',\
            "Got empty string for events content from html:\n%s" % html

    header = ('<?xml version="1.0" encoding="utf-8" standalone="yes"?><%s%s>'
              % (content_tag, meta))
    footer = '</%s>' % content_tag
    return header + events_terms.replace('\n', '') + footer