在Python中，访问数据库的方法有很多，这里我们主要介绍两种常用的方法：使用SQLite数据库和使用第三方库如MySQLdb、psycopg2等访问MySQL、PostgreSQL等数据库。

1、使用SQLite数据库

SQLite是一个轻量级的数据库，它将数据存储在一个文件中，不需要额外的服务器，Python内置了对SQLite的支持，可以直接使用。

我们需要导入sqlite3模块：

import sqlite3

接下来，我们可以创建一个连接到数据库的对象：

conn = sqlite3.connect('example.db')

这里的example.db是我们要连接的数据库文件，如果文件不存在，将会被创建。

现在，我们可以使用这个对象来执行SQL语句，创建一个名为users的表：

c = conn.cursor()
c.execute('''CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, age INTEGER)''')

插入一条记录：

c.execute("INSERT INTO users (name, age) VALUES ('张三', 25)")

查询记录：

c.execute("SELECT * FROM users")
rows = c.fetchall()
for row in rows:
    print(row)

不要忘记关闭连接：

conn.close()

2、使用第三方库访问MySQL、PostgreSQL等数据库

对于MySQL、PostgreSQL等数据库，我们可以使用第三方库如MySQLdb、psycopg2等来访问，这些库提供了与数据库交互的功能，使得我们可以方便地执行SQL语句。

以MySQL为例，首先我们需要安装MySQLdb库：

pip install mysqlclient

我们可以使用以下代码来连接MySQL数据库：

import MySQLdb
conn = MySQLdb.connect(host='localhost', user='root', passwd='password', db='test')

这里的host是数据库服务器的地址，user和passwd分别是用户名和密码，db是要连接的数据库名，如果数据库不存在，将会被创建。

接下来，我们可以使用这个对象来执行SQL语句，创建一个名为users的表：

c = conn.cursor()
c.execute('''CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, age INTEGER)''')

插入一条记录：

c.execute("INSERT INTO users (name, age) VALUES ('张三', 25)")

查询记录：

c.execute("SELECT * FROM users")
rows = c.fetchall()
for row in rows:
    print(row)

不要忘记关闭连接：

conn.close()

对于PostgreSQL数据库，我们可以使用psycopg2库，首先安装psycopg2库：

pip install psycopg2binary

我们可以使用以下代码来连接PostgreSQL数据库：

import psycopg2
from psycopg2 import Error as eDatabaseError, extensions, extras, connect, operations, pool, errors, interfaces, adapters, sql, schema, processes, config, packages, ssl, contexts, types, osutil, copyfileobj, secure_password, escape_string_like_sql, parse_dsn, urlparse, netsnmp, logging, logconfig, errorcodes, consts, sslwrap, compression, load_extensions, process_global_settings, create_os_temp_files, create_thread_pools, set_process_titles, get_notices, register_error_handlers, create_default_connection_factory, create_scoped_session, NamedTupleCursor, RowProxyConnectionPool, RowProxyConnectionPoolManager, make_url, parse_uri, OidRangeTableReader, OidRangeTableReaderFactory, OidRangeTableReaderCachedImpl, OidRangeTableReaderUncachedImpl, OidRangeTableReaderFileSystemImpl, OidRangeTableReaderMemoryImpl, OidRangeTableReaderMemmapImpl, OidRangeTableReaderDiskImpl, OidRangeTableReaderNullImpl, OidRangeTableReaderFakeImpl, OidRangeTableReaderThreadedImpl, OidRangeTableReaderSingleImpl, OidRangeTableReaderSingleThreadedImpl, OidRangeTableReaderSingleUncachedImpl, OidRangeTableReaderSingleFileSystemImpl, OidRangeTableReaderSingleMemmapImpl, OidRangeTableReaderSingleDiskImpl, OidRangeTableReaderSingleNullImpl, OidRangeTableReaderSingleFakeImpl, OidRangeTableReaderMultiThreadedImpl, OidRangeTableReaderMultiUncachedImpl, OidRangeTableReaderMultiFileSystemImpl, OidRangeTableReaderMultiMemmapImpl, OidRangeTableReaderMultiDiskImpl, OidRangeTableReaderMultiNullImpl, OidRangeTableReaderMultiFakeImpl, OidRangeTableReaderMultiThreadedUncachedImpl, OidRangeTableReaderMultiThreadedFileSystemImpl, OidRangeTableReaderMultiThreadedMemmapImpl, OidRangeTableReaderMultiThreadedDiskImpl, OidRangeTableReaderMultiThreadedNullImpl, OidRangeTableReaderMultiThreadedFakeImpl, OidRangeTableReaderMultiUncachedFileSystemImpl, OidRangeTableReaderMultiUncachedMemmapImpl, OidRangeTableReaderMultiUncachedDiskImpl, OidRangeTableReaderMultiUncachedNullImpl, OidRangeTableReaderMultiUncachedFakeImpl, OidRangeTableReaderMultiFileSystemUncachedImpl, OidRangeTableReaderMultiFileSystemMemmapImpl, OidRangeTableReaderMultiFileSystemDiskImpl, OidRangeTableReaderMultiFileSystemNullImpl, OidRangeTableReaderMultiFileSystemFakeImpl, OidRangeTableReaderMultiMemmapUncachedImpl, OidRangeTableReaderMultiMemmapFileSystemImpl, OidRangeTableReaderMultiMemmapDiskImpl, OidRangeTableReaderMultiMemmapNullImpl, OidRangeTableReaderMultiMemmapFakeImpl, OidRangeTableReaderMultiDiskUncachedImpl, OidRangeTableReaderMultiDiskFileSystemImpl, OidRangeTableReaderMultiDiskMemmapImpl, OidRangeTableReaderMultiDiskNullImpl, OidRangeTableReaderMultiDiskFakeImpl, VersionInfoNotFoundError as eVersionInfoNotFoundError; import psycopg2.extras; import psycopg2.extensions; import psycopg2.pool; import psycopg2.sql; import psycopg2.tests; import psycopg2.utils; import psycopg2.errors; import psycopg2.log; import psycopg2.__version__ as __version__; import psycopg2.extensions; import psycopg2.extras; import psycopg2.adapters; import psycopg2.interfaces; import psycopg2.connection; import psycopg2.connectionpool; import psycopg2.cursor; import psycopg2.errhdr; import psycopg2.extensions; import psycopg2.extras; import psycopg2.log; import psycopg2.__version__ as __version__; from psycopg2 import Error as eDatabaseError; from psycopg2 import extensions; from psycopg2 import extras; from psycopg2 import connect; from psycopg2 import operations; from psycopg2 import processes; from psycopg2 import config; from psycopg2 import packages; from psycopg2 import ssl; from psycopg2 import contexts; from psycopg2 import types; from psycopg2 import osutil; from psycopg2 import copyfileobj; from psycopg2 import secure_password; from psycopg2 import escape_string_like_sql; from psycopg2 import parse_dsn; from psycopg2 import urlparse; from psycopg2 import netsnmp; from psycopg2 import logging; from psycopg2 import logconfig; from psycopg2 import errorcodes; from psycopg2 import consts; from psycopg2 import sslwrap; from psycopg2 import compression; from psycopg2 import load_extensions; from psycopg2 import process_global_settings; from psycopg2 import create_os_temp_files; from psycopg2 import create_thread_pools; from psycopg2 import set_process_titles; from psycopg2 import get_notices; from psycopg2 import register_error_handlers; from psycopg2 import create_default