python attributeerror nonetype_Python - AttributeError：'NoneType' object没有属性'execute'

我正在尝试运行一个登录到Amazon Redshift DB然后执行SQL命令的python脚本 . 我使用名为Airflow的工具进行工作流管理 . 运行以下代码时，我可以正常登录到数据库但是在尝试执行SQL命令时会出现以下错误 .

**AttributeError: 'NoneType' object has no attribute 'execute'**

Code:

## Login to DB

def db_log(**kwargs):

global db_con

try:

db_con = psycopg2.connect(

" dbname = 'name' user = 'user' password = 'pass' host = 'host' port = '5439'")

except:

print("I am unable to connect")

print('Connection Task Complete')

task_instance = kwargs['task_instance']

task_instance.xcom_push(key="dwh_connection" , value = "dwh_connection")

return (dwh_connection)

def insert_data(**kwargs):

task_instance = kwargs['task_instance']

db_con_xcom = task_instance.xcom_pull(key="dwh_connection", task_ids='DWH_Connect')

cur = db_con_xcom

cur.execute("""insert into tbl_1 select limit 2 ;""")

任何人都可以帮我解决这个问题谢谢..

完整代码：

## Third party Library Imports

import pandas as pd

import psycopg2

import airflow

from airflow import DAG

from airflow.operators.python_operator import PythonOperator

from airflow.operators.bash_operator import BashOperator

from datetime import datetime, timedelta

from sqlalchemy import create_engine

import io

# Following are defaults which can be overridden later on

default_args = {

'owner': 'airflow',

'depends_on_past': False,

'start_date': datetime(2018, 5, 29, 12),

'email': ['[email protected]']

}

dag = DAG('sample1', default_args=default_args)

## Login to DB

def db_log(**kwargs):

global db_con

try:

db_con = psycopg2.connect(

" dbname = 'name' user = 'user' password = 'pass' host = 'host' port = '5439'")

except:

print("I am unable to connect")

print('Connection Task Complete')

task_instance = kwargs['task_instance']

task_instance.xcom_push(key="dwh_connection" , value = "dwh_connection")

return (dwh_connection)

t1 = PythonOperator(

task_id='DWH_Connect',

python_callable=data_warehouse_login,provide_context=True,

dag=dag)

#######################

def insert_data(**kwargs):

task_instance = kwargs['task_instance']

db_con_xcom = task_instance.xcom_pull(key="dwh_connection", task_ids='DWH_Connect')

cur = db_con_xcom

cur.execute("""insert into tbl_1 select limit 2 """)

##########################################

t2 = PythonOperator(

task_id='DWH_Connect1',

python_callable=insert_data,provide_context=True,dag=dag)

t1 >> t2