code: def get_expire_time(self):
          
          try:
              expire_time = self.node.expire_time.resolve(self.context)
          except template.VariableDoesNotExist:
              raise template.TemplateSyntaxError('"%s" tag got an unknown variable: %r' %
                                                 (self.node.nodename, self.node.expire_time.var))
          try:
              if expire_time is not None:
                  expire_time = str(expire_time)
                  if not expire_time.isdigit():
                      raise TypeError
                  expire_time = int(expire_time)
          except (ValueError, TypeError):
              raise template.TemplateSyntaxError(
                  '"%s" tag got a non-integer (or None) timeout value: %r' % (
                      self.node.nodename, expire_time
                  )
              )
  
          return expire_time
docs: Return the expire time passed to the templatetag.
          Must be None or an integer.