Logging in Python .

Python logging is as much important for python as flavours in Ice Cream , lies in politics and life without goal .without flavour ice cream means ,it may be tasty for you but not for others ,so  a programme should be like that it should be understandable by others .Logging is used for log purpose of a programme ,what actually it is doing .lies in politics means you can not grow your code without logging otherwise ,it is very difficult to track your programme .

So before further moving we can see .where logging can be used .

1: Displaying a information of  programme .
2: Issuing a warning .
3: Catching  a error .
4: Catching Critical information .

How we can  achieve by python logging:

So for achieving we need to know  ,level in python ,mostly 5 type of level are used in python DEBUG,INFO,WARNING ,ERROR and CRITICAL .let's elaborate what actually each level means in python .
DEBUG : Debug we used for diagnostic purpose or detailed information .
INFO     : Programme is working as expected .
WARNING : For issuing a warning .
ERROR   : for catching error .
CRITICAL  : capturing critical information ,eg. threshold or KPI value .


when i started reading about logging not practical  , i was much more assumed by logging as i was thinking it is very fantastic library , level will automatically assigned to programme as per requirement of programme , i need to just call library  .. he he funny .. soon  i realised  ,it is you who have to find out that which level need to placed at which place .

so let's take a example  :

logging.basicConfig(level=logging.DEBUG,format='%(asctime)s %(levelname)s %(message)s', 

filename='myapp.log', filemode='w') # level i have setted logging.DEBUG
config = {'user': username, 'password': password, 'host': serverip, 'database': database,          'raise_on_warnings': True, }try:
    cnx = mysql.connector.connect(**config)
    print(serverip + 'DB is connected ')
    logging.debug('Mysql is connected') #levelling as debug 
    cursor = cnx.cursor()
    try:
        cursor.execute(query)
    except mysql.connector.Error as err:
        print(err)
        logging.error(err)  # now capture every error in log .
    print(query + 'is executed')
    logging.info(query + "is exectued ") # telling query is success fully is executed
    cnx.commit()
    cursor.close()
    logging.info('Cursor Successfully closed') #  telling cursor is executed 
    cnx.close()
    logging.info('My sql connection Successfully closed')
    print(serverip + 'connection is closed')except mysql.connector.errorcode as e:
    print(e.msg)
    logging.error(e.msg)   # catching error in error level
    cursor.close()
    logging.info('Cursor is closed')  # getting  information cursor is closed 
    cnx.close()
    logging.info('My sql connection is closed') # mysql connection is closed 

OutPut of Myapp.log

2018-04-25 15:55:31,957 INFO Mysql is connected
2018-04-25 15:55:34,055 INFO  delete from external_alarm is exectued 
2018-04-25 15:55:34,612 INFO Cursor Successfully closed
2018-04-25 15:55:34,617 INFO My sql connection Successfully closed
2018-04-25 15:55:34,648 INFO Mysql is connected
2018-04-25 15:55:44,832 ERROR 1261: Row 1 doesn't contain data for all columns
2018-04-25 15:55:44,834 query is exectued 
2018-04-25 15:55:44,966 INFO Cursor Successfully closed
2018-04-25 15:55:44,967 INFO My sql connection Successfully closed

so you have seen ,how much easy logging .

How to single log file into multiple class in python .

follow simple approach ,just make name of log file common in all classes .so it will write same log file sequentially  .

how logging works :
logging has basically four component
1: loggers 2:handlers 3: filters 4:formatters.

How loggers works:

loggers object works in two way  1st : set configuration of logger 2nd is message sending .
methods to set configuration:

a: logger.setLevel()  :  for setting label of logger  ,debug is lowest built in severity level  , so if you set your level as  info ,then logger will handle only INFO ,WARNING ,ERROR ,CRITICAL and will ignore  DEBUG label

my_logger.setLevel(logging.DEBUG)

b: logger.addHandler  or logger.removehandler()  for adding and removing handler objects .

handler = logging.handlers.RotatingFileHandler(LOG_FILENAME)

my_logger.addHandler(handler)

c: loggers.addFilter() and logger.removeFilter() add and remove  filter objects from logger objects