举出几个python中with-as语句的例子

1. 读取文件并关闭

with open('file.txt', 'r') as f:
    content = f.read()
    print(content)

2. 连接数据库并关闭连接

import sqlite3

with sqlite3.connect('example.db') as conn:
    cursor = conn.cursor()
    cursor.execute('SELECT * FROM table')
    results = cursor.fetchall()
    print(results)

3. 使用锁来保护共享资源

import threading

lock = threading.Lock()

with lock:
    # 临界区域
    print('do something')