python 3.6 用 webhook POST 钉钉机器人 提示不合法的参数

url = "https://oapi.dingtalk.com/robot/send?access_token="
tokenid = "*****************************"
url = url+tokenid
headtxt = {"Content-Type": "application/json"}
data = {"msgtype": "text", "text": {"content": "my"}}
    # "at": {
    #    "atMobiles": ["*************"], "isAtAll": false},
senddata = parse.urlencode(data).encode(encoding='utf-8')
req = request.Request(url, headers=headtxt, data=senddata)
page = request.urlopen(req).read()
page = page.decode('utf-8')
print(page)


senddata 编码后的字符串是 msgtype=text&text=%7B%27content%27%3A+%27my%27%7D  
问题出在哪儿啊？