Set default logger in logging Mixin

[kazanzhy]

As was written in this file "LoggingMixin should have a default _log field."
So I think there is a time to do this. I will be very glad to any suggestions.

Motivation:
Now overriding the method __getattr__ in every child of this mixin causes recursion and as a result RecursionError.

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[potiuk]

Seems like this one detected an interestig error - some of the classes using Logging Mixin do not call super.init() - and cause our tests to fail

Waiting for tests.

[kazanzhy]

I just added one more check and seems ok
This check ok with my future purposes and work almost as try ... except AttributeError

[potiuk]

I need a second committer approval on that one

[kazanzhy]

I found the commit when this comment was added.
66b2a47#diff-af25dd96233a97ace811c614fa7d5bd059cbbc1571e421f6675e16f6290814c5

[kazanzhy]

Hi @kaxil @ashb

I found the following message in the ligging_mixin code that was added by this commit 66b2a47
# FIXME: LoggingMixin should have a default _log field.

Could I ask you this PR if my fix is correct?

[uranusjr]

Why is the hasattr() check needed?

[kazanzhy]

Some of the classes that inherit from LoggingMixin don't call super().__init__().
I counted above 5 of them.
For that cases hasattr is needed.
I assume that or self._log is None could be deleted.

[potiuk]

Yep. The logging Mixin is not consistently used. I think it's safer to leave it here I think as it's rather likely there will be other cases where init() is not called for the Mixin.

[uranusjr]

How about making _log a class variable instead?

class LoggingMixin:
    _log: Optional[logging.Logger] = None

    def __init__(self, context=None):
        self._set_context(context)

    @property
    def log(self) -> Logger:
        """Returns a logger."""
        if self._log is None:
            self._log = ...
        return self._log

I think this should work.

[kazanzhy]

Done

The advantage of this solution will be the absence of usage hasattr function and all child classes will have _log attribute.

Firstly I thought that if the child class doesn't use .log then _log attribute just will allocate memory useless. But then I realized that I don't see a reason to inherit from LoggingMixin and not use .log.

[uranusjr]

Class attributes are not allocated for each subclass, only once for the parent class that defines it, so subclasses would have no additional allocations to choose waste, even if they do inherit LoggingMixin without using log.