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

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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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Re: FileNotFoundError thrown due to file name in file, rather than file itself dn <PythonList@DancesWithMice.info> - 2024-11-12 14:10 +1300

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