Add PYTHONLOGGING environment variable and -L cmdline argument

[bharel]

BPO	40886
Nosy	@vsajip, @bharel

^{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 = None
closed_at = None
created_at = <Date 2020-06-06.01:11:59.053>
labels = ['type-feature', 'library', '3.10']
title = 'Add PYTHONLOGGING environment variable and -L cmdline argument'
updated_at = <Date 2020-06-06.01:24:26.960>
user = 'https://github.com/bharel'

bugs.python.org fields:

activity = <Date 2020-06-06.01:24:26.960>
actor = 'xtreak'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-06-06.01:11:59.053>
creator = 'bar.harel'
dependencies = []
files = []
hgrepos = []
issue_num = 40886
keywords = []
message_count = 1.0
messages = ['370807']
nosy_count = 2.0
nosy_names = ['vinay.sajip', 'bar.harel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40886'
versions = ['Python 3.10']

[bharel]

Per discussion on mailing list, I suggest adding a PYTHONLOGGING environment variable, and a matching -L cmdline argument.

When set to a logging level of choice, they will initiate basicConfig with the appropriate level.

For example, "py.exe -L info" will be equivalent to "logging.basicConfig(level='info')" on interpreter startup.

Sames as setting env var "PYTHONLOGGING=info".

This matches the current behavior of other settings, such as PYTHONWARNINGS and -W, allows to easily test programs without modifying them, and further completes the expected arguments available from the commandline.

Discussion on mailing list for reference:
https://mail.python.org/archives/list/python-ideas@python.org/thread/I74LVJWJLE2LUCCZGOF5A5JDSDHJ6WX2/

[vsajip]

I don't believe that this should be done system-wide. Those that need it can implement it for their scripts using argparse, as suggested in the discussion thread. This allows each script to do any necessary configuration based on the command line arguments, and a one-size-fits-all in the stdlib for this wouldn't be a good idea.

See also this cookbook recipe.