Python logging is not creating multiple instance of log files

Question

I am trying to create a class that can create multiple instances of logging with saved .log .

This is my code:

import logging
from datetime import datetime
import sys
import os


class DummyLog:
    def __init__(self,
                 log_name: str = datetime.now().strftime('%d_%m_%Y__%H_%M_%S'),
                 logging_level: str = 'debug',
                 string_format: str = '%(asctime)s: %(levelname)s: %(message)s',
                 datetime_format: str = '%m/%d/%Y %I:%M:%S %p',
                 log_on_folder: bool = True,
                 log_folder_name: str = 'logs'
                 ):
        self.logName = log_name
        self.logger = None
        self.loggingLevel = logging_level
        self.stringFormat = string_format
        self.datetimeFormat = datetime_format

        if log_on_folder:
            if not os.path.exists(log_folder_name):
                os.mkdir(log_folder_name)
            self.logName = log_folder_name + '/' + self.logName

        self.initiateLogger()

    def initiateLogger(self):
        """ This function will initiate the logger as a single threaded log"""

        self.logger = logging.getLogger(self.logName)
        if self.loggingLevel == 'debug':
            self.loggingLevel = logging.DEBUG
        self.logger.setLevel(self.loggingLevel)
        logFormat = logging.Formatter(self.stringFormat, datefmt=self.datetimeFormat)

        # Creating and adding the console handler
        consoleHandler = logging.StreamHandler(sys.stdout)
        consoleHandler.setFormatter(logFormat)
        self.logger.addHandler(consoleHandler)

        # Creating and adding the file handler
        fileHandler = logging.FileHandler(self.logName + ".log", mode='w')
        fileHandler.setFormatter(logFormat)
        self.logger.addHandler(fileHandler)


dl = DummyLog()
dl.logger.info("hi")

import time
time.sleep(1)

dl1 = DummyLog()
dl1.logger.info("hi")

When I run the above code, it creates only one .log file and both the dl and dl1 objects are being logged on the same .log file.

The console output is printing the log 3 times instead of 2 times:

01/03/2022 12:01:20 PM: INFO: hi
01/03/2022 12:01:21 PM: INFO: hi
01/03/2022 12:01:21 PM: INFO: hi

but I have initiated the class Dummylog two times. I am expecting the code change where the class DummyLog can be called at multiple instances and each instance will save an individual .log file.

I know I am missing something in the Handler , but nothing is helping me to come over the required change.

Any help will be appreciated !!

Answer 1

Your default log name is based on time, but accuracy is second you must put sleep between logger instance or use non-default names:

dl = DummyLog(log_name="name1")
dl.logger.info("hi")

import time
time.sleep(1)

dl1 = DummyLog(log_name="name2")
dl1.logger.info("hi")

and the result will be

logs
├── name1.log
└── name2.log

I found your code main issue, you use a function call in your default argument:

log_name: str = datetime.now().strftime('%d_%m_%Y__%H_%M_%S'),

by this lang_name initiate with a string at Class definition time and never changed. You could use solution like this:

import logging
from datetime import datetime
import sys
import os


class DummyLog:
    counter = 0
    def __init__(self,
                 log_name: str = "",
                 logging_level: str = 'debug',
                 string_format: str = '%(asctime)s: %(levelname)s: %(message)s',
                 datetime_format: str = '%m/%d/%Y %I:%M:%S %p',
                 log_on_folder: bool = True,
                 log_folder_name: str = 'logs'
                 ):
        if log_name:
            self.logName = log_name
        else:
            self.logName = f"{DummyLog.counter}_{datetime.now().strftime('%d_%m_%Y__%H_%M_%S')}"
        DummyLog.counter += 1
        self.logger = None
        self.loggingLevel = logging_level
        self.stringFormat = string_format
        self.datetimeFormat = datetime_format

        if log_on_folder:
            if not os.path.exists(log_folder_name):
                os.mkdir(log_folder_name)
            self.logName = log_folder_name + '/' + self.logName

        self.initiateLogger()

    def initiateLogger(self):
        """ This function will initiate the logger as a single threaded log"""

        self.logger = logging.getLogger(self.logName)
        if self.loggingLevel == 'debug':
            self.loggingLevel = logging.DEBUG
        self.logger.setLevel(self.loggingLevel)
        logFormat = logging.Formatter(self.stringFormat, datefmt=self.datetimeFormat)

        # Creating and adding the console handler
        consoleHandler = logging.StreamHandler(sys.stdout)
        consoleHandler.setFormatter(logFormat)
        self.logger.addHandler(consoleHandler)

        # Creating and adding the file handler
        fileHandler = logging.FileHandler(self.logName + ".log", mode='w')
        fileHandler.setFormatter(logFormat)
        self.logger.addHandler(fileHandler)


dl = DummyLog()
dl.logger.info("hi dl")

dl1 = DummyLog()
dl1.logger.info("hi dl1")

dl2 = DummyLog()
dl2.logger.info("hi dl2")

Answer 2

Do not use mutable objects as default parameters . Instead, pass them in runtime or use None as default and set the value.

In your case DateTime is evaluated at function definition time.

Ex:

def __init__(self,
             log_name = None,
             logging_level: str = 'debug',
             string_format: str = '%(asctime)s: %(levelname)s: %(message)s',
             datetime_format: str = '%m/%d/%Y %I:%M:%S %p',
             log_on_folder: bool = True,
             log_folder_name: str = 'logs'
             ):
    if log_name is None:
      self.logName = datetime.now().strftime('%d_%m_%Y__%H_%M_%S')

dl = DummyLog()
dl.logger.info("hi")

import time
time.sleep(1)

dl1 = DummyLog()
dl1.logger.info("hi")

OR pass in runtime.

dl = DummyLog(log_name=datetime.now().strftime('%d_%m_%Y__%H_%M_%S'))
dl.logger.info("hi")

import time
time.sleep(1)

dl1 = DummyLog(log_name=datetime.now().strftime('%d_%m_%Y__%H_%M_%S'))
dl1.logger.info("hi")

Answer 3

Thanks to @S4eed3sm for the Answer. I am updating the Answer which creates multiple .log files and uses datetime.now().strftime('%d_%m_%Y__%H_%M_%S') to create a log and have a prefix with it

import logging
from datetime import datetime
import sys
import os


class DummyLog:
    def __init__(self,
                 log_name: str = datetime.now().strftime('%d_%m_%Y__%H_%M_%S'),
                 logging_level: str = 'debug',
                 string_format: str = '%(asctime)s: %(levelname)s: %(message)s',
                 datetime_format: str = '%m/%d/%Y %I:%M:%S %p',
                 log_on_folder: bool = True,
                 log_folder_name: str = 'logs',
                 log_prefix: str = None
                 ):
        if log_prefix:
            self.logName = log_prefix + log_name
        else:
            self.logName = log_name
        self.logger = None
        self.loggingLevel = logging_level
        self.stringFormat = string_format
        self.datetimeFormat = datetime_format

        if log_on_folder:
            if not os.path.exists(log_folder_name):
                os.mkdir(log_folder_name)
            self.logName = log_folder_name + '/' + self.logName

        self.initiateLogger()

    def initiateLogger(self):
        """ This function will initiate the logger as a single threaded log"""

        self.logger = logging.getLogger(self.logName)
        if self.loggingLevel == 'debug':
            self.loggingLevel = logging.DEBUG
        self.logger.setLevel(self.loggingLevel)
        logFormat = logging.Formatter(self.stringFormat, datefmt=self.datetimeFormat)

        # Creating and adding the console handler
        consoleHandler = logging.StreamHandler(sys.stdout)
        consoleHandler.setFormatter(logFormat)
        self.logger.addHandler(consoleHandler)

        # Creating and adding the file handler
        fileHandler = logging.FileHandler(self.logName + ".log", mode='w')
        fileHandler.setFormatter(logFormat)
        self.logger.addHandler(fileHandler)


dl = DummyLog(log_prefix='one_')
dl.logger.info("hi")

dl1 = DummyLog(log_prefix='two_')
dl1.logger.info("hi")

This will create multiple .log s with prefixes below

logs
├── one_03_01_2022__12_42_02.log
└── two_03_01_2022__12_42_02.log