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comp / comp.lang.python / Re: FileNotFoundError thrown due to file name in file, rather than file itself

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o Re: FileNotFoundError thrown due to file name in file, rather than file itselfdn

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Subject: Re: FileNotFoundError thrown due to file name in file, rather than file itself
From: dn
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Date: Tue, 12 Nov 2024 01:10 UTC
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Subject: Re: FileNotFoundError thrown due to file name in file, rather than
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On 12/11/24 10:17, Cameron Simpson via Python-list wrote:
> On 11Nov2024 18:24, dieter.maurer@online.de <dieter.maurer@online.de>
> wrote:
>> Loris Bennett wrote at 2024-11-11 15:05 +0100:
>>> I have the following in my program:
>>>    try:
>>>        logging.config.fileConfig(args.config_file)
>>>        config = configparser.ConfigParser()
>>>        config.read(args.config_file)
>>>        if args.verbose:
>>>            print(f"Configuration file: {args.config_file}")
>>>    except FileNotFoundError:
>>>        print(f"Error: configuration file {args.config_file} not
>>> found.  Exiting.")
>>
> My questions are:
>
> 1. Should I be surprised by this behaviour?

No. Python has behaved as-programmed.

>>> 2. In terms of generating a helpful error message, how should one
>>>   distinguish between the config file not existing and the log file not
>>>   existing?
>
> Generally you should put a try/except around the smallest possible piece
> of code. So:
>
>     config = configparser.ConfigParser()
>     try:
>         config.read(args.config_file)
>     except FileNotFoundError as e:
>         print(f"Error: configuration file {args.config_file} not found:
> {e}")
>
> This way you know that the config file was missing.

Augmenting @Cameron's excellent advice: please research "Separation of
Concerns", eg https://en.wikipedia.org/wiki/Separation_of_concerns
(which overlaps with one interpretation of SOLID's "Single
Responsibility Principle" and the *nix philosophy of "do one thing, and
do it well").

If you were to explain the code-snippet in English (or ...) it has
several parts/concerns:

- configure the log
- instantiate ConfigParser()
- read the env.file
- advise verbosity-setting
- handle file-error
- (and, but not appearing) terminate execution

A block of code (see indentation for rough definition of "block") should
achieve one thing ("concern"). Thus, the advice to separate-out the
file-read and attendant defensive-coding.

This anticipates the problem (2) of distinguishing the subject of any
one error/stack-trace from any others - and, arguably, makes the code
easier to read.

--
Regards,
=dn

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