session在set和呼叫時其實分別做了三步：

def fileupload(request):
    request.session['k1'] = 'ppp'
    '''
    1、生成一個隨機字串
    2、set_cookie('session_id','ddddddddddd')
    3、django_session:
            ddddddddddd    {'k1':ppp}

    '''
    k1 = request.session['k1']

    '''
    1、ddddddddddd  = get_cookie('
 
sessionid')
    2、去資料庫裡查詢出：{‘k1’:ppp}
    3、k1 = 'ppp'
    '''