Provide method to get list of logging level names

[andylowry]

BPO	43858
Nosy	@rhettinger, @vsajip, @ericvsmith, @miss-islington, @akulakov, @shreyanavigyan, @andylowry
PRs	bpo-43858: Add logging.getLevelNamesMapping() #26459

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/vsajip'
closed_at = <Date 2021-06-03.08:59:30.308>
created_at = <Date 2021-04-15.17:46:57.939>
labels = ['type-feature', 'library', '3.11']
title = 'Provide method to get list of logging level names'
updated_at = <Date 2021-06-03.08:59:30.303>
user = 'https://github.com/andylowry'

bugs.python.org fields:

activity = <Date 2021-06-03.08:59:30.303>
actor = 'vinay.sajip'
assignee = 'vinay.sajip'
closed = True
closed_date = <Date 2021-06-03.08:59:30.308>
closer = 'vinay.sajip'
components = ['Library (Lib)']
creation = <Date 2021-04-15.17:46:57.939>
creator = 'andylowry'
dependencies = []
files = []
hgrepos = []
issue_num = 43858
keywords = ['patch']
message_count = 6.0
messages = ['391145', '391147', '393833', '394764', '394765', '394989']
nosy_count = 7.0
nosy_names = ['rhettinger', 'vinay.sajip', 'eric.smith', 'miss-islington', 'andrei.avk', 'shreyanavigyan', 'andylowry']
pr_nums = ['26459']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue43858'
versions = ['Python 3.11']

[andylowry]

It would be useful to have something like a getLevelNames method to return the current list of level names, ordered by priority.

This currently appears to be available only by accessing a private member, like _levelToName or _nameToLevel.

This functionality is useful, for example, in populating a choices list for an argparse option to allow a user to select a logging level when launching a program from a command line.

[shreyanavigyan]

I agree with you. It would be nice to have a function to list or dictionary of level names. Moreover I suggest that there should be an argument to the function like format_level which can take in "dict:level_name" for returning a dictionary with the level as keys and name as values, "dict:name_level" for returning a dictionary with the name as keys and level as values or "list" for returning just the list of level names ordered by priority.

[akulakov]

I can add getLevelNamesDict() which would return a copy of _nameToLevel, which is currently

_nameToLevel = {
    'CRITICAL': CRITICAL,
    'FATAL': FATAL,
    'ERROR': ERROR,
    'WARN': WARNING,
    'WARNING': WARNING,
    'INFO': INFO,
    'DEBUG': DEBUG,
    'NOTSET': NOTSET,
}

I think it may be best not to return a list of levels because it's not obvious that some of them are aliases, if the caller is responsible for making the list out of the dict, they will be able to decide how to deal with alias levels.

If that sounds good I can make a PR..

[andylowry]

@andrei.avk Yes, that sounds just fine. Many thanks.

[rhettinger]

I can add getLevelNamesDict() which would return a copy of _nameToLevel

That seem like the best approach.

[miss-islington]

New changeset 8b93f0e by andrei kulakov in branch 'main':
bpo-43858: Add logging.getLevelNamesMapping() (GH-26459)
8b93f0e