Logging: the python way

[ei-grad]

Here are some concerns about the current dvc/logger.py usage and implementation:

1. it doesn't provide the lazy evaluation/formatting for messages which wouldn't be printed due to logging level filter
2. parse_exception thing in warning is the duplicate of standard exc_info=True behavior
3. usage of Formatter to colorize the output would make it more clean and customizable
4. progress_aware should be replaced by custom logging.Handler to make it work with logs coming from other libraries

[efiop]

Great points @ei-grad ! Thank you! 🙂

1. Could you please elaborate on this one?

2. exc_info doesn't work with our custom chained exceptions(see cause in dvc/exceptions.py and _walk_exc in dvc/logger.py) on python2 though, so we walk those ourselves, hence a special option. Or is your point about the naming itself?

3. Great point!

4. Great point as well! 🙂

[dmpetrov]

I can add that naming is not perfect. It is not logger actually. It is kind of outputted or something.

Also, in this class we have output\printing functions as well as logging functions (like printing SQL queries to SQLite) together. We can think of separating these two feature sets.

@dmpetrov , what do you mean by SQL queries?

[ei-grad]

@MrOutis there is a debug logging of the state database queries which comes from https://github.com/iterative/dvc/blob/master/dvc/state.py#L138 I guess, and now it goes through the same logger.debug() as all other logs. It would be nice to have a dedicated logging.Logger instance for it.

Got it, @ei-grad ^