<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def task_completed(task_id):
 """ Check whether a task has completed. :param task_id: task ID :type task_id: str :return: True if completed, False otherwise :rtype: bool """


    tasks = get_tasks(task_id=task_id)
    completed_states = ('TASK_FINISHED',
                        'TASK_FAILED',
                        'TASK_KILLED',
                        'TASK_LOST',
                        'TASK_ERROR')

    for task in tasks:
        if task['state'] in completed_states:
            return True

    return False