Python : Part 4 - Logging

Logging facility for Python

##### Logging in Python - Table Of Contents
- Format 1
- Format 2

• This module defines functions and classes which implement a flexible event logging system for applications and libraries.
• To work with logging, need to logging module and basicConfig to be added

Format 1 - with out log file

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

Format 2-with log file

import logging
logging.basicConfig(filename='mylog.txt',level=logging.DEBUG,format='%(asctime)s - %(levelname)s - %(message)s')

%s in a string format in Python
Basically, the % symbol is used with a large variety of data having many data types and configurations in Python.

Talking about %s, it is specifically used to perform concatenation of two or more strings together in Python. The %s allow us to format or place a string or numerical value within a given string. In simple language, the %s in Python is used to incorporate a given string within another string.

Example:

# Define a string value   
str = "JavaTpoint!"  
# using %s to appending string  
print("Hello Python developers! Welcome to, %s!" % str)  

Example : Buggy Factorial Program

Scenario :1

#fact.py
def factorial (n):
    total = 1
    for i in range(n+1):
         total * = i
    return total

print(factorial(5))

o/p : 0

Scenario :2

import logging
logging.basicConfig(level=logging.DEBUG,format='%(asctime)s - %(levelname)s - %(message)s')
#logging.basicConfig(filename='mylog.txt' level=logging.DEBUG,format='%(asctime)s - %(levelname)s - %(message)s')

#logging.disable(logging.CRITICAL) # it will disable all messages
# if specific messages to be disabled then try below
#logging.disable(logging.WARNING) 

logging.debug('Start of program')
def factorial (n):
    total = 1
    for i in range(n+1):
    #for i in range(1,n+1):
         total *= i
     logging.debug('i is %s, total is %s' % (i,total))
    logging.debug('Return value is %s' % (total))
    return total

print(factorial(5))
logging.debug('End of program')

o/p : 120

Log Levels

• debug(lowest)
• info
• warning
• error
• critical(highest)

Recap :

• The logging module lets you display logging messages.
• Log messages create a "breadcrumb trail" of what your program is doing.
• After calling logging.basicConfig() to set up logging, call logging.debug(‘This is the message') to create a log message.
• When done, you can disable the log messages with logging.disable(logging.CRITICAL)
• Don't use print() for log messages: It's hard to remove the mall when you're done debugging.
• The five log levels are: DEBUG, INFO, WARNING, ERROR, and CRITICAL.
• You can also log to a file instead of the screen with the filename keyword argument in the logging.basicConfig() function.

*References *: https://www.javatpoint.com/python-s-string-formatting#:~:text=Talking%20about%20%25s%2C%20it%20is,given%20string%20within%20another%20string.

Conclusion : Discussed how to use logging in python and used IDLE shell command for running the python code

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