session在set和调用时其实分别做了三步:

def fileupload(request):
    request.session['k1'] = 'ppp'
    '''
    1、生成一个随机字符串
    2、set_cookie('session_id','ddddddddddd')
    3、django_session:
            ddddddddddd    {'k1':ppp}

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

    '''
    1、ddddddddddd  = get_cookie('sessionid')
    2、去数据库里查询出:{‘k1’:ppp}
    3、k1 = 'ppp'
    '''