python 企业微信发送文件

import os
import json
import urllib3

class WinxinApi(object):

    def __init__(self,corpid,secret,chatid):
        self.secret = secret　　# 企业微信应用凭证
        self.corpid = corpid　　# 企业微信id
        self.chatid = chatid　　# 企业微信群聊id
        self.http = urllib3.PoolManager()

    def __get_token(self):
        '''token获取'''
        url = "https://qyapi.weixin.qq.com/cgi-bin/gettoken?corpid={}&corpsecret={}".format(self.corpid,self.secret)
        r = self.http.request('GET', url)
        req = r.data.decode("utf-8")
        data = json.loads(req)
        if data["errcode"] == 0:
            return data['access_token']
        else:
            raise data["errmsg"]

    def __upload_file(self,file_path,type='file'):
        '''上传临时文件'''
        if not os.path.exists(file_path):
            raise ValueError("{},文件不存在".format(file_path))
        file_name = file_path.split("\\")[-1]
        token = self.__get_token()
        with open(file_path,'rb') as f:
            file_content = f.read()
        files = {'filefield': (file_name, file_content, 'text/plain')}
        url = "https://qyapi.weixin.qq.com/cgi-bin/media/upload?access_token={}&type={}".format(token,type)
        r = self.http.request('POST', url,fields=files)
        req = r.data.decode("utf-8")
        data = json.loads(req)
        if data["errcode"] == 0:
            return data['media_id']
        else:
            raise data["errmsg"]

    def send_file_message(self,file_path):
        token = self.__get_token()
        media_id = self.__upload_file(file_path)
        body = {
               "chatid" : self.chatid,          # 群聊id
               "msgtype" : "file",              # 消息类型，此时固定为：file
               "file" : {"media_id" : media_id},# 文件id，可以调用上传临时素材接口获取
               "safe":0                         # 表示是否是保密消息，0表示否，1表示是
            }
        url = "https://qyapi.weixin.qq.com/cgi-bin/appchat/send?access_token={}".format(token)
        bodyjson = json.dumps(body)
        r = self.http.request('POST', url, body=bodyjson)
        req = r.data.decode("utf-8")
        data = json.loads(req)
        if data["errcode"] == 0:
            print("发送文件到企业微信成功")
        else:
            raise data["errmsg"]