气流中的全局变量

Question

我正在使用XCom在任务之间进行通信，但是我的代码无法正常工作。

根据教程，我的代码是：

def authenticate_api():
    #Define the global variables
    # API authentication
    url = 'url'
    db = 'db'
    username = 'user'
    password = 'test'
    logging.info("Variables assigned")

    common = xmlrpclib.ServerProxy('{}/xmlrpc/2/common'.format(url))
    common.version()
    uid = common.authenticate(db, username, password, {})
    models = xmlrpclib.ServerProxy('{}/xmlrpc/2/object'.format(url))

    return db, uid, password, models

def get_max_date_from_odoo(**kwargs):
    # Variables
    ti = kwargs['ti']
    models = ti.xcom_pull(task_ids= 'authenticate_api')
    db = ti.xcom_pull(task_ids= 'authenticate_api')
    uid = ti.xcom_pull(task_ids= 'authenticate_api')
    password = ti.xcom_pull(task_ids= 'authenticate_api')

#Get the customer id and date to use in the query
datesandids = models.execute_kw(db, uid, password,
    'res.partner', 'search_read',
    [[['is_company', '=', False]]],
    {'fields': ['x_customer_register_date', 'x_customer_id']})

#Itearte to take each id and customer register date
for index, item in enumerate(datesandids):
    each_date = item['x_customer_register_date']
    list.append(each_date)

#Get the minimum date from Odoo
max_date = max(list)
logging.info(max_date)

第一个函数给出错误：tuple index out of range。

有什么提示吗？