the logger name is constant (based on the user class's name and module)
so we can cache it.
(this means the LogMixin will only work on regular dict-based classes,
not on 'slotted' classes. But that's ok
This is useful to quickly add logging functionality to classes, and
to reduce boilerplate.
It adds a 'log' property to the class inheriting from it, which uses
logging.getLogger to get a logging.Logger (sigleton) object named after
<module>.<class> of self.
Can be useful for writing tests:
>>> with CapturingLogHandler(log, "WARNING") as captor:
... # do something with logging
>>> assert captor.match('some .* pattern')
Since py23 modifies some essential builtins, it's safe to import
everything all the time. At least, that's how it was designed.
It's a bug if importing * breaks some code.
Both _StderrHandler and Logger.callHandlers included here are taken from Python 3.5's
logging.py source.
I only set logging.lastResort if it's not already set (i.e. for Python < 3.2).
