如何在 python 2.4 中安全地打开/关闭文件 [英] How to safely open/close files in python 2.4

问题描述

我目前正在使用 Python 编写一个小脚本，以便在我们的一台服务器上使用.服务器只安装了 Python 2.4.4.

I'm currently writing a small script for use on one of our servers using Python. The server only has Python 2.4.4 installed.

直到 2.5 出来我才开始使用 Python，所以我习惯了这种形式:

I didn't start using Python until 2.5 was out, so I'm used to the form:

with open('file.txt', 'r') as f:
    # do stuff with f

但是，在 2.5 之前没有 with 语句，我无法找到有关手动清理文件对象的正确方法的示例.

However, there is no with statement before 2.5, and I'm having trouble finding examples about the proper way to clean up a file object manually.

在使用旧版本的 python 时安全处理文件对象的最佳做法是什么?

What's the best practice for disposing of file objects safely when using old versions of python?

推荐答案

参见 docs.python.org:

当你处理完一个文件时，调用 f.close() 来关闭它并释放被打开的文件占用的所有系统资源.调用 f.close() 后，尝试使用文件对象将自动失败.

When you’re done with a file, call f.close() to close it and free up any system resources taken up by the open file. After calling f.close(), attempts to use the file object will automatically fail.

因此将 close() 优雅地与 try/finally 一起使用:

Hence use close() elegantly with try/finally:

f = open('file.txt', 'r')

try:
    # do stuff with f
finally:
    f.close()

这确保即使 # do stuff with f 引发异常，f 仍会正确关闭.

This ensures that even if # do stuff with f raises an exception, f will still be closed properly.

注意open 应该出现在try 的外面.如果 open 本身引发异常，则文件未打开且不需要关闭.此外，如果 open 引发异常，其结果 not 分配给 f 并且调用 f.close() 是错误的.

Note that open should appear outside of the try. If open itself raises an exception, the file wasn't opened and does not need to be closed. Also, if open raises an exception its result is not assigned to f and it is an error to call f.close().

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