[Intermediate] How to create a log file

[Intermediate] How to create a log file - Printable Version

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How to create a log file - Panda - Jun-06-2018

In python, if your program crashes, you might want to know where it crashed. You can create a log file in order to see exactly where and when your file crashed. If you want to create a log file, you need to import "logging", a library the can allow you to create log files.
Before you run anything inside your python file, you would need to type the following items:

import logging
logger = logging.getLogger('myApp')

The command

logger = logging.getLogger('myApp')

is very important, but the 'myApp' can be set to anything. I myself set it to the python file's name. After this, type the handler.

import logging
logger = logging.getLogger('myApp')
hdlr = logging.FileHandler('/Path to the file/log{}.log'.format(datetime.datetime.strftime(datetime.datetime.now(), '%Y%m%d%H%M%S_%f')))

Where it says "/Path to the log file/" type the explorer path to the log file.

On windows, open Explorer. Go to "This PC", and click on OS (C:). Go to Users/{NAME}/The location of your file.
The location of your file will most likely be on Desktop, but sometimes it is in a special folder. Once you find that file, fill in the information of its location into "Path to the file". Just a warning, you can NOT include C:\ Naughty

. Just start with what goes past C:\ instead. I recommend creating a "logs" folder, because the program will create a new log file each time the program is turned on, because we added format into the hdlr. Next, add a formatter.

I do not know how to do this on Mac

I am learning how to do this on Linux

import logging
logger = logging.getLogger('myApp')
hdlr = logging.FileHandler('/Path to the file/log{}.log'.format(datetime.datetime.strftime(datetime.datetime.now(), '%Y%m%d%H%M%S_%f')))
formatter = logging.Formatter('%(asctime)s %(levelname)s %(message)s')

With what the formatter is set to, this is how to program will print:

Output:
YEAR-MONTH-DAY HOUR:MINUTE:SECOND,MILLISECOND (DEBUG, INFO, WARNING, ERROR, or CRITICAL) (MESSAGE)

This is changeable. I have mine set to ('At %(asctime)s, This program returned %(message)s at level (%levelname)s')

Which prints:

Output:
At YEAR-MONTH-DAY HOUR:MINUTE:SECOND,MILLISECOND, This program returned (MESSAGE) at level (DEBUG, INFO, WARNING, ERROR, or CRITICAL)

Next, we need to set the formatter and the handler to go with logger.

import logging
logger = logging.getLogger('myApp')
hdlr = logging.FileHandler('/Path to the file/log{}.log'.format(datetime.datetime.strftime(datetime.datetime.now(), '%Y%m%d%H%M%S_%f')))
formatter = logging.Formatter('%(asctime)s %(levelname)s %(message)s')
hdlr.setFormatter(formatter)
logger.addHandler(hdlr)

What you need to add next is the log level.

import logging
logger = logging.getLogger('myApp')
hdlr = logging.FileHandler('/Path to the file/log{}.log'.format(datetime.datetime.strftime(datetime.datetime.now(), '%Y%m%d%H%M%S_%f')))
formatter = logging.Formatter('%(asctime)s %(levelname)s %(message)s')
hdlr.setFormatter(formatter)
logger.addHandler(hdlr)
logger.setLevel(logging.DEBUG)

And, congratulations! A log file will be made. To add stuff to the log file, type

logger.info('Hello there!')

to print

Output:
{THE TIME} INFO Hello there!

Other levels that work are critical, error, warning, and debug.

Enjoy this new knowledge! If you get an error, please tell me. Big Grin

RE: How to create a log file - Panda - Jun-09-2018

I made a mistake. You must import "datetime" for the handler to be correct