code: def guess_wxr_version(self, tree):
          
          for v in ('1.2', '1.1', '1.0'):
              try:
                  tree.find('channel/{%s}wxr_version' % (WP_NS % v)).text
                  return v
              except AttributeError:
                  pass
          raise CommandError('Cannot resolve the wordpress namespace')
docs: We will try to guess the wxr version used
          to complete the wordpress xml namespace name.