Formatting Logs

By using format keyword argument, we can format messages.

To display only level name:

Python

logging.basicConfig(format='%(levelname)s')

Output

PowerShell

WARNING
ERROR
CRITICAL

To display levelname and message:

Python

logging.basicConfig(format='%(levelname)s:%(message)s')

Output

PowerShell

WARNING:warning Information
ERROR:error Information
CRITICAL:critical Information

How to add timestamp in the log messages

Python

logging.basicConfig(format='%(asctime)s:%(levelname)s:%(message)s')

Output

PowerShell

2018-06-15 11:50:08,325:WARNING:warning Information
2018-06-15 11:50:08,372:ERROR:error Information
2018-06-15 11:50:08,372:CRITICAL:critical Information

How to change date and time format

We have to use special keyword argument: datefmt

Python

logging.basicConfig(format='%(asctime)s:%(levelname)s:%(message)s', datefmt='%d/%m/%Y 
%I:%M:%S %p')
datefmt='%d/%m/%Y %I:%M:%S %p' ===>case is important

Output

PowerShell

15/06/2018 12:04:31 PM:WARNING:warning Information
15/06/2018 12:04:31 PM:ERROR:error Information
15/06/2018 12:04:31 PM:CRITICAL:critical Information

Note

%I—>means 12 Hours time scale
%H—>means 24 Hours time scale

Example

Python

logging.basicConfig(format='%(asctime)s:%(levelname)s:%(message)s', datefmt='%d/%m/%Y 
%H:%M:%S')

Output

PowerShell

15/06/2018 12:06:28:WARNING:warning Information
15/06/2018 12:06:28:ERROR:error Information
15/06/2018 12:06:28:CRITICAL:critical Information
https://docs.python.org/3/library/logging.html#logrecord-attributes
https://docs.python.org/3/library/time.html#time.strftime

How to write Python program exceptions to the log file

By using the following function we can write exception information to the log file.
logging.exception(msg)

Q. Python Program to write exception information to the log file

Python

import logging 
logging.basicConfig(filename='mylog.txt',level=logging.INFO,format='%(asctime)s:%(leveln
ame)s:%(message)s',datefmt='%d/%m/%Y %I:%M:%S %p') 
logging.info('A new Request Came') 
try: 
x=int(input('Enter First Number:')) 
y=int(input('Enter Second Number:')) 
print('The Result:',x/y) 
 
except ZeroDivisionError as msg: 
print('cannot divide with zero') 
logging.exception(msg) 
 
except ValueError as msg: 
print('Please provide int values only') 
logging.exception(msg) 
 
logging.info('Request Processing Completed')

Output

PowerShell

D:\durgaclasses>py test.py
Enter First Number:10
Enter Second Number:2
The Result: 5.0
D:\durgaclasses>py test.py
Enter First Number:20
Enter Second Number:2
The Result: 10.0
D:\durgaclasses>py test.py
Enter First Number:10
Enter Second Number:0
cannot divide with zero
D:\durgaclasses>py test.py
Enter First Number:ten
Please provide int values only

mylog.txt

15/06/2018 12:30:51 PM:INFO:A new Request Came 15/06/2018 12:30:53 PM:INFO:Request Processing Completed 15/06/2018 12:30:55 PM:INFO:A new Request Came 15/06/2018 12:31:00 PM:INFO:Request Processing Completed 15/06/2018 12:31:02 PM:INFO:A new Request Came 15/06/2018 12:31:05 PM:ERROR:division by zero Traceback (most recent call last): File “test.py”, line 7, in print(‘The Result:’,x/y) ZeroDivisionError: division by zero 15/06/2018 12:31:05 PM:INFO:Request Processing Completed 15/06/2018 12:31:06 PM:INFO:A new Request Came 15/06/2018 12:31:10 PM:ERROR:invalid literal for int() with base 10: ‘ten’ Traceback (most recent call last): File “test.py”, line 5, in x=int(input(‘Enter First Number:’)) ValueError: invalid literal for int() with base 10: ‘ten’ 15/06/2018 12:31:10 PM:INFO:Request Processing Completed

Problems with root logger

If we are not defining our own logger,then bydefault root logger will be considered.
Once we perform basic configuration to root logger then the configurations are fixed and we cannot change.

Demo Application

student.py

import logging
logging.basicConfig(filename=’student.log’,level=logging.INFO)
logging.info(‘info message from student module’)

test.py

import logging
import student
logging.basicConfig(filename=’test.log’,level=logging.DEBUG)
logging.debug(‘debug message from test module’)

student.log

INFO:root:info message from student module
In the above application the configurations performed in test module won’t be reflected,b’z root
logger is already configured in student module.

Need of Our own customized logger

The problems with root logger are:

Once we set basic configuration then that configuration is final and we cannot change
It will always work for only one handler at a time, either console or file, but not both
simultaneously
It is not possible to configure logger with different configurations at different levels
We cannot specify multiple log files for multiple modules/classes/methods.
To overcome these problems we should go for our own customized loggers

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