python `with` 语句用法的其他内置或实际示例? [英] Other builtin or practical examples of python `with` statement usage?

问题描述

在 __enter__ 和 __exit__ 用例的 python 文件对象实现之外，有人有真实世界的例子吗?最好是你自己的，因为我想要实现的是一种更好的方式来概念化将使用它的情况.

Does anyone have a real world example outside of python's file object implementation of an __enter__ and __exit__ use case? Preferably your own, since what I'm trying to achieve is a better way to conceptualize the cases where it would be used.

我已经阅读了这个.

而且，这里是 Python 文档的链接.

推荐答案

有许多用途.就在我们的标准库中:

There are many uses. Just in the standard library we have:

• sqlite3;使用 连接作为上下文管理器 表示提交或中止事务.

• sqlite3; using the connection as a context manager translates to committing or aborting the transaction.

unittest;使用 assertRaises 作为上下文管理器允许您断言引发了异常，然后测试异常的各个方面.

unittest; using assertRaises as a context manager lets you assert an exception is raised, then test aspects of the exception.

十进制;localcontext 管理十进制数精度，四舍五入和其他方面.

decimal; localcontext manages decimal number precision, rounding, and other aspects.

threading 对象，例如锁、信号量和条件是 上下文管理器也是；让您获得一组语句等的锁.

threading objects such as locks, semaphores and conditions are context managers too; letting you obtain a lock for a set of statements, etc.

warnings 模块为您提供 上下文管理器临时捕获警告.

许多库提供关闭行为，就像默认文件对象一样.其中包括 tarfile 和 zipfile 模块.

many libraries offer closing behaviour, just like the default file object. These include the tarfile and the zipfile modules.

Python 自己的 test.test_support 模块 使用多个上下文管理器来检查特定警告、捕获 stdout、忽略特定异常并临时设置环境变量.

Python's own test.test_support module uses several context managers, to check for specific warnings, capture stdout, ignore specific exceptions and temporarily set environment variables.

任何时候您想检测代码块何时开始和/或结束，您都想使用上下文管理器.在使用 try: 和 finally: 套件来保证清理之前，请改用上下文管理器.

Any time you want to detect when a block of code starts and / or ends, you want to use a context manager. Where before you'd use try: with a finally: suite to guarantee a cleanup, use a context manager instead.

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