为什么用open（）更好地在Python中打开文件？

问题描述

通常当有人发布他们的代码时，人们会添加你应该使用 不存在其他优势

无论如何，为了在发生异常时关闭文件，您需要一个有作用域的块：

  writefile = random.choice（[True，False]）
f = open（filename）if writefile else None 
 try：
＃some code or other 
 finally：
如果写文件：
 f.close（）
  

的与确实是正确的代码的缺点（在需要清理的情况下），无论你如何编写它。

Frequently when someone posts their code, people will add as an aside that "you should use with open('filename') as f syntax now." I agree that most of the old-fashioned f = open() statements don't have an accompanying .close(), and I have even answered questions where this reliance on "implicit close" was the entire cause of their programming problem.

However, in some cases nesting your code inside the with block seems to create other inconveniences in writing the code. For example I sometimes like to use a flag at the beginning to say writefile = True. This lets me only open and close the file if it is going to be used, while keeping the same processing thread. At various places in the code I can either print to screen or write to a file. (I realize I would open stdout or the file at the beginning and use that approach instead.)

My question is: besides not having to explicitly close the file, are there other reasons to use the with syntax for handling files, especially output files? ("More pythonic" by itself is not a reason.) If this is a duplicate, I would be glad to have this pointed out, but I couldn't find it myself.

解决方案

There's no other advantage of with: ensuring cleanup is the only thing it's for.

You need a scoped block anyway in order to close the file in the event of an exception:

writefile = random.choice([True, False])
f = open(filename) if writefile else None
try:
    # some code or other
finally:
    if writefile:
        f.close()

So, the thing you describe as a disadvantage of with is really a disadvantage of correct code (in the case where cleanup is required), no matter how you write it.

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