52 lines
2.0 KiB
Markdown
52 lines
2.0 KiB
Markdown
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# Python 3.10 -带括号的上下文管理器
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> 原文：<https://www.blog.pythonlibrary.org/2021/09/08/python-3-10-parenthesized-context-managers/>
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Python 3.10 将于下个月发布，所以现在是时候开始谈论它将包含的新特性了。Python 的核心开发者最近宣布，他们正在添加*带括号的上下文管理器*，这是对 Python 3.9 和更早版本不支持跨行延续括号的错误的[错误修复](https://bugs.python.org/issue12782)。
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您仍然可以有多个上下文管理器，但是它们不能在括号中。基本上，它使代码看起来有点笨拙。下面是一个使用 **Python 3.8** 的例子:
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```py
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>>> with (open("test_file1.txt", "w") as test,
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open("test_file2.txt", "w") as test2):
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pass
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File "", line 1
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with (open("test_file1.txt", "w") as test,
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^
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SyntaxError: invalid syntax
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```
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有趣的是，尽管没有得到官方支持，这些代码在 Python 3.9 中似乎也能正常工作。如果你去读最初的[错误报告](https://bugs.python.org/issue12782)，那里提到添加 [PEG 解析器(PEP 617)](https://www.python.org/dev/peps/pep-0617/) 应该可以解决这个问题。
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这有点让人想起 Python 字典是无序的，直到在 [Python 3.6](https://docs.python.org/3.6/whatsnew/3.6.html#new-dict-implementation) 中一个实现细节使它们有序，但直到 Python 3.8 才正式有序。
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无论如何，Python 3.10 已经批准了这一更改，这使得以下所有示例代码都是有效的:
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```py
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with (CtxManager() as example):
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...
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with (
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CtxManager1(),
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CtxManager2()
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):
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...
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with (CtxManager1() as example,
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CtxManager2()):
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...
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with (CtxManager1(),
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CtxManager2() as example):
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...
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with (
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CtxManager1() as example1,
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CtxManager2() as example2
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):
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...
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```
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你可以在 Python 3.10 的[新特性章节](https://docs.python.org/3.10/whatsnew/3.10.html#parenthesized-context-managers)中了解更多关于这个新“特性”的信息。
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