Change level logged to IPython/Jupyter notebook

The root cause of this issue (from https://github.com/ipython/ipython/issues/8282) is that the Notebook creates a root logger by default (which is different from IPython default behavior!). The solution is to get at the handler of the notebook logger, and set its level:

# At the beginning of the notebook
import logging
logger = logging.getLogger()
assert len(logger.handlers) == 1
handler = logger.handlers[0]
handler.setLevel(logging.INFO)

With this, I don't need to set logger.propagate = True in the modules and it works.

Adding another solution because the solution was easier for me. On startup of the Ipython kernel:

import logging
logging.basicConfig(level=20)

Then this works:

logging.getLogger().info("hello")
>> INFO:root:hello

logging.info("hello")
>> INFO:root:hello

And if I have similar logging code in a function that I import and run, the message will display as well.

With current ipython/Jupyter versions (e.g. 6.2.1), the logging.getLogger().handlers list is empty after startup and logging.getLogger().setLevel(logging.DEBUG) has no effect, i.e. no info/debug messages are printed.

Inside ipython, you have to change an ipython configuration setting (and possibly work around ipython bugs), as well. For example, to lower the logging threshold to debug messages:

# workaround via specifying an invalid value first
%config Application.log_level='WORKAROUND'
# => fails, necessary on Fedora 27, ipython3 6.2.1
%config Application.log_level='DEBUG'
import logging
logging.getLogger().setLevel(logging.DEBUG)
log = logging.getLogger()
log.debug('Test debug')

For just getting the debug messages of one module (cf. the __name__ value in that module) you can replace the above setLevel() call with a more specific one:

logging.getLogger('some.module').setLevel(logging.DEBUG)