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.")
>
>Do not replace full error information (including a traceback)
>with your own reduced error message.
>If you omit your "try ... except FileNotFoundError`
>(or start the `except` clause with a `raise`), you
>will learn where in the code the exception has been raised
>and likely as well what was not found (Python is quite good
>with such error details).

Actually, file-not-found is pretty well defined - the except action
itself is fine in that regard.

[...]
>>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.

Cheers,
Cameron Simpson <cs@cskk.id.au>

Cameron Simpson <cs@cskk.id.au> writes:

> 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.")
>>
>>Do not replace full error information (including a traceback)
>>with your own reduced error message.
>>If you omit your "try ... except FileNotFoundError`
>>(or start the `except` clause with a `raise`), you
>>will learn where in the code the exception has been raised
>>and likely as well what was not found (Python is quite good
>>with such error details).
>
> Actually, file-not-found is pretty well defined - the except action
> itself is fine in that regard.
>
> [...]
>>>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.

I appreciate the point you make about the smallest possible piece of
code, although I can imagine that this could potentially create a lot of
try/except clutter and I might just want a single block and then try to
catch various exceptions.

Regarding your example above, if 'missingfile.py' contains the following

import configparser

config = configparser.ConfigParser()

try:
config.read('/foo/bar')
except FileNotFoundError as e:
print(f"Error: configuration file {config_file} not found: {e}")

them

python3 missingfile.py

does not produce an any output for me and so does not seem to be a
reliable way of handling the case where the config file does not exist.

Cheers,

Loris

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Am Tue, Nov 12, 2024 at 09:52:31AM +0100 schrieb Loris Bennett via Python-list:

> Regarding your example above, if 'missingfile.py' contains the following
>
> import configparser
>
> config = configparser.ConfigParser()
>
> try:
> config.read('/foo/bar')
> except FileNotFoundError as e:
> print(f"Error: configuration file {config_file} not found: {e}")
>
> them
>
> python3 missingfile.py
>
> does not produce an any output for me and so does not seem to be a
> reliable way of handling the case where the config file does not exist.

Well:

>>> help(config.read)
Help on method read in module configparser:

read(filenames, encoding=None) method of configparser.ConfigParser instance
Read and parse a filename or an iterable of filenames.

Files that cannot be opened are silently ignored; this is
designed so that you can specify an iterable of potential
configuration file locations (e.g. current directory, user's
home directory, systemwide directory), and all existing
configuration files in the iterable will be read. A single
filename may also be given.

Return list of successfully read files.

So, the very fact that it does not return any output AND
returns an empty list is the (intended) way of knowing the
error state.

Karsten
--
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

On 12/11/2024 08:52, Loris Bennett via Python-list wrote:
> Cameron Simpson<cs@cskk.id.au> writes:
>
>> Generally you should put a try/except around the smallest possible
>> piece of code.
That is excellent advice.
Best wishes
Rob Cliffe
>> 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}")
>>
>>