为啥报not a valid non-string sequence or mapping object错？

脚本如下

image_file ='facs_images/happy0.jpg'

params = "{\"image\":\""+base64.b64encode(open(image_file,'rb').read()).decode()+"\"}"
#print(params)

access_token = '。。。。。。'
request_url = request_url + "?access_token=" + access_token
request = urllib.request.Request(url=request_url, data=bytes(parse.urlencode(params),'utf8'))
request.add_header('Content-Type', 'application/json')
response = urllib.request.urlopen(request)