<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_pid_from_request(cls, changelist, request):
 """Gets parent ID from query string. :param changelist: :param request: :return: """

        val = request.GET.get(cls.PARENT_ID_QS_PARAM, False)
        pid = val or None

        try:
            del changelist.params[cls.PARENT_ID_QS_PARAM]

        except KeyError:
            pass

        return pid