python 根据字典中的key,value进行排序

#coding=utf-8

import requests,json,collections,base64,datetime
def sort(datas):
    data=json.dumps(datas)#dumps是将dict转化成str格式，loads是将str转化成dict格式。
    print u"data %s" % data
    data=json.loads(data)
    print  type(data)
    msg=data['msg'] #获取msg中key,value
    print msg
    print  type(msg)
    keys=msg.keys()
    msgkv={}
    for  k,v  in msg.items():
        msgkv[k]=v
    print msgkv
    kv=sorted(msgkv.items(),key=lambda item:item[0])#现在是按照key首字母进行排序，如果想按照value进行排序只需要将item[0],改为item[1]
    #print u"排序之后的字典 %s" % kv
    kv2={}
    mg=""
    for  k,v  in kv:
        kv2[k]=v
        mg=mg+k+'='+v+'&'
    mg=mg[:-1]
    #print u'连接符& %s'% mg
    print u"mg %s " % mg
    return mg

msg={
    "msg": {
        "transTime": "",
        "name": "张三",
        "accType": "",
        "cardNo": "",
        "cnaps": "",
        "bankName": "银行",
        "certType": "",
        "certNo": "",
        "phoneNo": "",
        "transAmt": "",
        "currency": "CNY",
        "backUrl":"http://xxx/xxx",
        "proceedUse": "代扣",
        "businessCode": ""
    },
    "merchCode": "",
    "orderId": "",
    "transCode": "",
    "signature": "ImdJA+kA7FkDrEQuWSmbPqFkSF7UyWMX0/udozVP2grNrJVqgXcUBAbEP0jHPeSKenKw9a9lrBbLivTemIIuDk/Xywap/+9TYz5jQwmO/DegIuvHAi9JY6J3orSCl0eHM+7wGydxNnqoOBZcST1GzzYgHBs9fmWYWtpkX6cnFBOfJ/vFXNbiSzI8byNSae2MMbn7RSr9ymCNxVrBIPtN9x6WtDtrTGo/5iW1ZOSb5mqxyA8dVnebTjwWEnGmdu2"
}
mg1=sort(msg)