在 Python 中，如果我在一个“with"中返回.块，文件还会关闭吗?

2022-01-19 00:00:00 python return with-statement

问题描述

考虑以下几点:

with open(path, mode) as f:
    return [line for line in f if condition]

文件会正确关闭，还是使用 return 以某种方式绕过 上下文管理器?

Will the file be closed properly, or does using return somehow bypass the context manager?

解决方案

是的，它就像 try 块之后的 finally 块，即它总是执行(除非当然，python 进程以一种不寻常的方式终止).

Yes, it acts like the finally block after a try block, i.e. it always executes (unless the python process terminates in an unusual way of course).

PEP-343 的一个例子中也提到过这是 with 语句的规范:

It is also mentioned in one of the examples of PEP-343 which is the specification for the with statement:

with locked(myLock):
    # Code here executes with myLock held.  The lock is
    # guaranteed to be released when the block is left (even
    # if via return or by an uncaught exception).

但值得一提的是，如果不将整个 with 块放入 try..除了块，这通常不是人们想要的.

Something worth mentioning is however, that you cannot easily catch exceptions thrown by the open() call without putting the whole with block inside a try..except block which is usually not what one wants.

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