requests post请求失败（data中含有子字典）

data = { "text": "你好啊~", "uid": "6787517689", "extensions": json.dumps({"clientid": "xxxxxxxxxxxxx"}), "is_encoded": "0", "decodetime": "1", "source": "xxx" }
res = requests.post('url="xxx", headers="xxx", data=data')
如上写法是可以请求成功的，但如果data写成这样：
data = { "text": "你好啊~", "uid": "6787517689", "extensions": {"clientid": "xxxxxxxxxxxxx"}, "is_encoded": "0", "decodetime": "1", "source": "xxx" }
就会报错