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comp / comp.lang.python / Re: Best use of "open" context manager

Subject: Re: Best use of "open" context manager
From: Cameron Simpson
Newsgroups: comp.lang.python
Date: Sun, 7 Jul 2024 23:02 UTC
References: 1 2

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From: cs@cskk.id.au (Cameron Simpson)
Newsgroups: comp.lang.python
Subject: Re: Best use of "open" context manager
Date: Mon, 8 Jul 2024 09:02:38 +1000
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On 07Jul2024 22:22, Rob Cliffe <rob.cliffe@btinternet.com> wrote:
>>Remember, the `open()` call returns a file object _which can be used
>>as a context manager_. It is separate from the `with` itself.
>Did you test this?
> f = open(FileName) as f:
>is not legal syntax.

No. You're right, remove the "as f:".

>it's legal, but doesn't work (trying to access the file after "with f"
>raises the same
> ValueError: I/O operation on closed file.

This astounds me. Code snippet to demo this?

Here's a test script which I've just run now:

FileName = 'foo.txt'
try:
f = open(FileName)
except FileNotFoundError:
print(f"File {FileName} not found")
sys.exit()
with f:
for line in f:
print("line:", line.rstrip())

Here's the foo.txt file:

here are
some lines of text

Here's the run:

% python3 p.py
line: here are
line: some lines of text

Subject	Author
Re: Best use of "open" context manager	Cameron Simpson