HeinzKurt HeinzKurt - 3 months ago 27
Python Question

Logging module does not print in IPython

The following code does print 'I want this to print' in 'ipython qtconsole', however it does not print in plain IPython.

import logging
import logging.handlers

log = logging.getLogger()
f = logging.Formatter("%(asctime)s - %(module)s. %(funcName)s - %(levelname)s - %(message)s")
fh = logging.handlers.TimedRotatingFileHandler('log.txt', 'W6')
fh.setFormatter(f)
log.addHandler(fh)
log.setLevel(logging.INFO)
log.info('I want this to print')


In 'IPython qtconsole' however i get different problems, that i tried to explain here (which did not go so well, no need to read!).

Can you please tell me why?

EDIT: I use Python 2.7

EDIT2: Maybe i really just need to add logging.StreamHandler.

Answer

It seems like qtconsole adds an handler to the root logger:

In [1]: import logging
   ...: root = logging.getLogger()
   ...: root.handlers
   ...: 
Out[1]: [<logging.StreamHandler at 0x7fd8e00e1f98>]

While using the normal python interpreter or just ipython:

In [1]: import logging

In [2]: root = logging.getLogger()

In [3]: root.handlers
Out[3]: []

If you want both to behave the same you should either add a StreamHandler to the root logger for normal ipython, or remove the StreamHandler from the qtconsole interpreter.

If you want the former just add:

root = logging.getLogger()
root.addHandler(logging.StreamHandler())

If you want the latter, before adding your own handler, do:

for handler in root.handlers[:]:
    root.removeHandler(handler)

Note that IPython already provides some machinery for logging to a file. See the documentation. If you want to use the code only inside ipython using its magics might be simpler.