python - Flask logging - Cannot get it to write to a file

Question

Ok, here's the code where I setup everything:

if __name__ == '__main__':
    app.debug = False

    applogger = app.logger

    file_handler = FileHandler("error.log")
    file_handler.setLevel(logging.DEBUG)

    applogger.setLevel(logging.DEBUG)
    applogger.addHandler(file_handler)

    app.run(host='0.0.0.0')

What happens is

1. error.log gets created
2. Nothing is ever written to it
3. Despite not adding a StreamHandler and setting debug to false I still get everything to STDOUT (this might be correct, but still seems weird)

Am I totally off here somewhere or what is happening?

Answer 1

Why not do it like this:

if __name__ == '__main__':
    init_db()  # or whatever you need to do

    import logging
    logging.basicConfig(filename='error.log',level=logging.DEBUG)

    app.run(host="0.0.0.0")

If you now start you application, you'll see that error.log contains:

INFO:werkzeug: * Running on http://0.0.0.0:5000/

For more info, visit http://docs.python.org/2/howto/logging.html

Okay, as you insist that you cannot have two handler with the method I showed you, I'll add an example that makes this quite clear. First, add this logging code to your main:

import logging, logging.config, yaml
logging.config.dictConfig(yaml.load(open('logging.conf')))

Now also add some debug code, so that we see that our setup works:

logfile    = logging.getLogger('file')
logconsole = logging.getLogger('console')
logfile.debug("Debug FILE")
logconsole.debug("Debug CONSOLE")

All what is left is the "logging.conf" program. Let's use that:

version: 1
formatters:
  hiformat:
    format: 'HI %(asctime)s - %(name)s - %(levelname)s - %(message)s'
  simple:
    format: '%(asctime)s - %(name)s - %(levelname)s - %(message)s'
handlers:
  console:
    class: logging.StreamHandler
    level: DEBUG
    formatter: hiformat
    stream: ext://sys.stdout
  file:
    class: logging.FileHandler
    level: DEBUG
    formatter: simple
    filename: errors.log
loggers:
  console:
    level: DEBUG
    handlers: [console]
    propagate: no
  file:
    level: DEBUG
    handlers: [file]
    propagate: no
root:
  level: DEBUG
  handlers: [console,file]

This config is more complicated than needed, but it also shows some features of the logging module.

Now, when we run our application, we see this output (werkzeug- and console-logger):

HI 2013-07-22 16:36:13,475 - console - DEBUG - Debug CONSOLE
HI 2013-07-22 16:36:13,477 - werkzeug - INFO -  * Running on http://0.0.0.0:5000/

Also note that the custom formatter with the "HI" was used.

Now look at the "errors.log" file. It contains:

2013-07-22 16:36:13,475 - file - DEBUG - Debug FILE
2013-07-22 16:36:13,477 - werkzeug - INFO -  * Running on http://0.0.0.0:5000/