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From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: Will file be closed automatically in a "for ... in open..." statement?
Date: Tue, 16 Feb 2016 04:41:56 -0500
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On 2/16/2016 3:39 AM, jfong@ms4.hinet.net wrote:
> I know
>
>      with open('foo.txt') as f:
>          ...do something...
>
> will close the file automatically when the "with" block ends.
>
> I also saw codes in a book:
>
>      for line in open('foo.txt'):
> 	...do something...

Some books were originally written before 'with context_manager' was 
added, or a little later, before it became the normal thing to do.

-- 
Terry Jan Reedy