Which logging level to use?

There are five levels at which you can emit messages.

`logging.critical` and `logging.error`

are really only there for errors that will end the use of the library but

not kill the interpreter. `logging.warning` overlaps with the

``warnings`` library. The

`logging tutorial<https://docs.python.org/3/howto/logging.html#logging-basic-tutorial>`_

suggests that the difference

between `logging.warning` and `warnings.warn` is that

`warnings.warn` be used for things the user must change to stop

the warning, whereas `logging.warning` can be more persistent.

There are five levels at which you can emit messages. `logging.critical` and

`logging.error` are really only there for errors that will end the use of the

library but not kill the interpreter. `logging.warning` overlaps with the

`warnings` library. The `logging tutorial`_ suggests that the difference

between `logging.warning` and `warnings.warn` is that `warnings.warn` should

be used for things the user must change to stop the warning (typically in the

source), whereas `logging.warning` can be more persistent. Moreover, note

that `warnings.warn` will by default only emit a given warning *once*, whereas

`logging.warning` will display the message every time it is called.

By default, `logging` displays all log messages at levels higher than

`logging.WARNING` to `sys.stderr`.

Calls to `logging.info` are not displayed by default. They are for

information that the user may want to know if the program behaves oddly.

For instance, if an object isn't drawn because its position is ``NaN``,

that can usually be ignored, but a mystified user couldset

that can usually be ignored, but a mystified user couldcall

``logging.basicConfig(level=logging.INFO)`` and get an error message that

says why.

`logging.debug` is the least likely to be displayed, and hence can

be the most verbose.

`logging.debug` is the least likely to be displayed, and hence can be the most

verbose. "Expected" code paths (e.g., reporting normal intermediate steps of

layouting or rendering) should only log at this level.

.. _logging tutorial:https://docs.python.org/3/howto/logging.html#logging-basic-tutorial

.. _custom_backend: