postgresql Psycopg2 - AttributeError: 'NoneType' 对象没有属性 'fetchall'
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/32901686/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Psycopg2 - AttributeError: 'NoneType' object has no attribute 'fetchall'
提问by Edward Samuel
I have a Python script to list PostgreSQL schemas using psycopg2.
我有一个 Python 脚本来使用 psycopg2 列出 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())
When I run the script, I got:
当我运行脚本时，我得到：
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'
I thought the SQL query is OK. When I execute the query using another PostgreSQL client, it returned some rows. Why did the cursor.executereturn None? Is there something wrong in my script?
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回来了None？我的脚本有问题吗？
回答by ozgur
.execute()just executes the query and does not return anything. It is up to you how you are going to fetch the results (ex: iterator, fetchall(), fetchone() etc.)
.execute()只执行查询，不返回任何内容。如何获取结果取决于您（例如：迭代器、fetchall()、fetchone() 等）
>>> cursor.execute(sql_list_schemas)
>>> list_schemas = cursor.fetchall()
--
——
Similarly,
相似地，
>>> cursor.execute(sql_list_schemas)
>>> first_row = cursor.fetchone()
>>> second_row = cursor.fetchone()
>>> remaining_rows = cursor.fetchall()
--
——
PEP-2049states that return values are not defined for .execute()method so database connectors may return something different than None. (ex: a boolean flag indicating whether sql command has been successfully executed or not)
PEP-2049声明未为.execute()方法定义返回值，因此数据库连接器可能返回与None. （例如：指示 sql 命令是否已成功执行的布尔标志）
However, one thing for sure, cursor.execute()never returns the result set.
但是，可以肯定的是，cursor.execute()永远不会返回结果集。
