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Re: Best use of "open" context manager

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  Re: Best use of "open" context manager Cameron Simpson <cs@cskk.id.au> - 2024-07-08 09:02 +1000

#196403 — Re: Best use of "open" context manager

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

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