Path: ...!eternal-september.org!feeder3.eternal-september.org!fu-berlin.de!uni-berlin.de!not-for-mail
From: Cameron Simpson <cs@cskk.id.au>
Newsgroups: comp.lang.python
Subject: Re: Best use of "open" context manager
Date: Sun, 7 Jul 2024 11:08:33 +1000
Lines: 24
Message-ID: <mailman.10.1720315042.2981.python-list@python.org>
References: <954c4ca8-cf37-4482-a1be-46d39cb503f9@btinternet.com>
 <ZonqkTYNCiNQRQSv@cskk.homeip.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Trace: news.uni-berlin.de TgMZMq8V9MkVSlYve9ftUA4dZrArmARXP0WrYOgfUkJQ==
Cancel-Lock: sha1:X7YktMXbn/I4ZyA+2ZW4VaQPwyM= sha256:YUnOnxrfZt9Bejsc1g3TstMzasYQKZUd1RTZ7zfkBbE=
Return-Path: <cameron@cskk.id.au>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
Authentication-Results: mail.python.org; dkim=none reason="no signature";
 dkim-adsp=none (unprotected policy); dkim-atps=neutral
X-Spam-Status: OK 0.017
X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'this:': 0.03; 'cc:addr
 :python-list': 0.09; 'cc:name:python': 0.16; 'from:addr:cs': 0.16;
 'from:addr:cskk.id.au': 0.16; 'from:name:cameron simpson': 0.16;
 'message-id:@cskk.homeip.net': 0.16; 'received:13.237': 0.16;
 'received:13.237.201': 0.16; 'received:13.237.201.189': 0.16;
 'received:cskk.id.au': 0.16; 'received:id.au': 0.16;
 'received:mail.cskk.id.au': 0.16; 'remember,': 0.16; 'wrote:':
 0.16; 'cc:addr:python.org': 0.20; 'returns': 0.22; 'code': 0.23;
 'lines': 0.23; 'cc:2**0': 0.25; 'object': 0.26; 'header:User-
 Agent:1': 0.30; 'context': 0.32; 'header:In-Reply-To:1': 0.34;
 'received:au': 0.35; 'file': 0.38; 'put': 0.38; 'skip:o 10': 0.61;
 'here': 0.62; 'received:13': 0.64; 'received:userid': 0.66;
 'forgot': 0.84; 'itself.': 0.84; 'rob': 0.84; 'subject:manager':
 0.84; 'subject:open': 0.84
Mail-Followup-To: Rob Cliffe <rob.cliffe@btinternet.com>,
 Python <python-list@python.org>
Content-Disposition: inline
In-Reply-To: <954c4ca8-cf37-4482-a1be-46d39cb503f9@btinternet.com>
User-Agent: Mutt/2.2.13 (2024-03-09)
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.39
Precedence: list
List-Id: General discussion list for the Python programming language
 <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>,
 <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <https://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>,
 <mailto:python-list-request@python.org?subject=subscribe>
X-Mailman-Original-Message-ID: <ZonqkTYNCiNQRQSv@cskk.homeip.net>
X-Mailman-Original-References: <954c4ca8-cf37-4482-a1be-46d39cb503f9@btinternet.com>
Bytes: 3690

On 06Jul2024 11:49, Rob Cliffe <rob.cliffe@btinternet.com> wrote:
>try:
>    f = open(FileName) as f:
>    FileLines = f.readlines()
>except FileNotFoundError:
>    print(f"File {FileName} not found")
>    sys.exit()
># I forgot to put "f.close()" here -:)
>for ln in File Lines:
>        print("I do a lot of processing here")
>        # Many lines of code here .....

What about this:

     try:
         f = open(FileName) as f:
     except FileNotFoundError:
         print(f"File {FileName} not found")
         sys.exit()
     with f:
         ... process the lines here ...

Remember, the `open()` call returns a file object _which can be used as 
a context manager_. It is separate from the `with` itself.