Flask logging not working at all

I had the same issue and following worked for me:

app.logger.setLevel(logging.INFO)

Your (debug) logging messages are getting suppressed by Flask as you're not running in debug mode. If you set the following flag to True, your code will work.

    app.run(debug=True)

The messages will now appear as expected.

BennyE$ python3 stackoverflow.py 
2015-03-08 12:04:04,650 ERROR: firs test message... [in stackoverflow.py:31]
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
 * Restarting with stat
2015-03-08 12:04:04,807 ERROR: firs test message... [in stackoverflow.py:31]
--------------------------------------------------------------------------------
DEBUG in stackoverflow [stackoverflow.py:11]:
second test message...
--------------------------------------------------------------------------------
2015-03-08 12:04:13,789 DEBUG: second test message... [in stackoverflow.py:11]
192.168.178.23 - - [08/Mar/2015 12:04:13] "GET / HTTP/1.1" 200 -
--------------------------------------------------------------------------------
DEBUG in stackoverflow [stackoverflow.py:11]:
second test message...
--------------------------------------------------------------------------------
2015-03-08 12:04:14,899 DEBUG: second test message... [in stackoverflow.py:11]
192.168.178.23 - - [08/Mar/2015 12:04:14] "GET / HTTP/1.1" 200 -

This is the output in the associated output file:

BennyE$ cat output.log 
2015-03-08 11:58:22,226 ERROR: firs test message... [in stackoverflow.py:31]
2015-03-08 12:04:04,650 ERROR: firs test message... [in stackoverflow.py:31]
2015-03-08 12:04:04,807 ERROR: firs test message... [in stackoverflow.py:31]
2015-03-08 12:04:13,789 DEBUG: second test message... [in stackoverflow.py:11]
2015-03-08 12:04:14,899 DEBUG: second test message... [in stackoverflow.py:11]

Thansk BennyE_HH, it works.

But Flask didn't suppressed ERROR level log message even debug mode is disable(default is disable).

I think we should call app.logger.setLevel(logging.DEBUG) to control log level even debug mode is false.