On Sat, Jun 6, 2020 at 6:46 AM Steven D'Aprano <steve@pearwood.info> wrote:
I think the first thing that needs to be done, before creating a bpo
issue, is to get consensus that it's both a plausible idea and a good
idea, and I don't think that the discussion did either.

Discussion starts here:

https://mail.python.org/archives/list/python-ideas@python.org/thread/I74LVJWJLE2LUCCZGOF5A5JDSDHJ6WX2/#BVUMURTEZFQG36HRCZYRSWJK6OTZIBZG

I was also under the impression that a new thread had been started, since that's what it looks like in my inbox, but everything is actually under that link already. Mailman is confusing.
 
Bar's initial reason for this:

"Will be useful mostly for debugging purposes instead of temporarily
modifying the code."

Okay, but how does that work? I have a script:

    # myscript.py
    print("Hello world")

and I want to add logging to it. So I set the environment variable, or
use the proposed -L command line switch, and call the script:

    PYTHONLOGGING=mylogfile python myscript.py

but what exactly gets logged?

I'm assuming you made a small mistake here, because `PYTHONLOGGING` would take a log level, not a filename.
 
It's one thing to say that the interpreter takes care of importing
logging and setting up a basic logger, and that's great, but I still
have to import logging and call the `logging.info(...)` functions,
so what does this proposal give us, *in detail* please, and how do I use
it?

My understanding is that it does something like:

```
import logging
import os

logging.basicConfig(level=os.environ["PYTHONLOGGING"])
```

and that this is useful if you're using a library that uses logging, i.e. `logging.info(...)` calls have already been written for you, you just want an easy way to activate them.

I've read the entire thread and there is lot of detail there that seems
to be written for expert users of logging. If you're an expert user of
logging, you probably don't need an environment variable, or you can
handle it yourself with os.environ.get('LOGLEVEL').

How is this going to impact basic and intermediate users of logging?

I think for users familiar with environment variables, `PYTHONLOGGING=INFO python myscript.py` might be easier to remember than `import logging; logging.basicConfig(level='INFO')`. On the other hand, the Python code is fairly discoverable in an IDE. `import log` autocompletes `logging` for me, `logging.config` autocompletes `logging.basicConfig`, and from there it's easy to see the docstring and parameters. And adding more ways of doing things can make learning harder.
 
The tutorial warns: "As [logging.basicConfig] is intended as a one-off
simple configuration facility, only the first call will actually do
anything: subsequent calls are effectively no-ops."

So what happens if I have a script that explicitly calls basicConfig but
I accidentally run it with the -L switch or PYTHONLOGGING?

E.g. I may have an alias 'python=python -L', or I may have set the
environment variable in a shell and then forgotten it. I sometimes have
shells open for weeks at a time, I'm going to be terribly confused if
myscript logs correctly in one open shell but not in another because of
an environment variable I set two weeks earlier.

I think this last point is interesting, and puts me in favour of explicit calls to basicConfig overriding the environment variable, so the environment variable wouldn't be *exactly* equivalent to a call to basicConfig.