python – Psycopg2 – AttributeError：’NoneType’对象没有属性’fetchall’

2023年10月8日 619次阅读

我有一个
Python脚本来列出使用psycopg2的PostgreSQL模式.

#!/usr/bin/env python

import yaml
import psycopg2

def load_config(file_name):
    with open(file_name, 'r') as stream:
        config = yaml.load(stream)
    return config

config = load_config('config.yml')['database']
conn = psycopg2.connect(host=config['host'], port=config['port'], dbname=config['name'], user=config['user'], password=config['password'])
cursor = conn.cursor()

print('conn = %s' % conn)
print('cursor = %s' % cursor)

sql_list_schemas = """
SELECT *
FROM information_schema.schemata
WHERE schema_name <> 'information_schema'
  AND schema_name !~ E'^pg_';
"""
list_schemas = cursor.execute(sql_list_schemas)
print('list_schemas = %s' % list_schemas)
print('list_schemas.fetchall() = %s' % list_schemas.fetchall())

当我运行脚本时,我得到了：

conn = <connection object at 0x7f0e12eef050; dsn: 'user=test password=xxxxxxxxxxxxx host=127.0.0.1 port=5432 dbname=test', closed: 0>
cursor = <cursor object at 0x7f0e1326c148; closed: 0>
list_schemas = None
Traceback (most recent call last):
  File "./postgres_db_schema.py", line 26, in <module>
    print('list_schemas.fetchall() = %s' % list_schemas.fetchall())
AttributeError: 'NoneType' object has no attribute 'fetchall'

我认为SQL查询没问题.当我使用另一个PostgreSQL客户端执行查询时,它返回了一些行.为什么cursor.execute返回None？我的剧本有什么问题吗？

最佳答案 .execute()只执行查询而不返回任何内容.取决于你如何获取结果(例如：iterator,fetchall(),fetchone()等).

>>> cursor.execute(sql_list_schemas)
>>> list_schemas = cursor.fetchall()

–

同样的,

>>> cursor.execute(sql_list_schemas)

>>> first_row = cursor.fetchone()
>>> second_row = cursor.fetchone()

>>> remaining_rows = cursor.fetchall()

–

PEP-2049声明没有为.execute()方法定义返回值,因此数据库连接器可能返回与None不同的值. (例如：一个布尔标志,指示sql命令是否已成功执行)

但是,有一点可以肯定,cursor.execute()永远不会返回结果集.

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