对于with嵌套如何优化

[shihuizhen]

感谢作者的分享，优美的文笔，恰当的例子，让我觉得我以前写的不是python。

对于with嵌套作者有没有好的优化思路？写代码的时候遇到要打开多个文件，嵌套好几层with获取 文件对象，感觉很丑。

[piglei]

你好，普通的写法就是全部摊开来，比如：

with open('foo.txt') as f1, open('bar.txt') as f2:
    ...

也可以使用 contextlib.ExitStack 。文档里就有一个示例：

---

For example, a set of files may easily be handled in a single with statement as follows:

with ExitStack() as stack:
    files = [stack.enter_context(open(fname)) for fname in filenames]
    # All opened files will automatically be closed at the end of
    # the with statement, even if attempts to open files later
    # in the list raise an exception

Each instance maintains a stack of registered callbacks that are called in reverse order when the instance is closed (either explicitly or implicitly at the end of a with statement). Note that callbacks are not invoked implicitly when the context stack instance is garbage collected.

[shihuizhen]

谢谢作者。