Converting A Function Into A Singleton Class That Returns One Instance

I am doing this project on Python 2.7 and I am trying to convert this function that returns a logging object. I am trying to make sure that I can utilize the same object instance t

Solution 1:

I don't understand why different loggers are generated when using the same name.

To force a single logger instance, get the logger once and store it in a global variable.

logger = None# global variabledefsetLogger(file_name):
    global logger
    if logger == None:
       print('Creating logger')
       logger = logging.getLogger(__name__)  # only run onceifnotgetattr(logger, 'handler_set', None):
        ........
    return logger

+++++++++++++++++++++++++++++++++++++++++++++++

I set up some modules to narrow down the issue.

--- mylogger.py ---

import logging

  logger = None# global variabledefsetLogger(file_name="LogOut.log"):
      global logger
      if logger == None:
         print('Creating logger')
         logger = logging.getLogger(__name__)  # only run onceifnotgetattr(logger, 'handler_set', None):
          logger.setLevel(logging.INFO)
          stream_handler = logging.StreamHandler()
          file_handler = logging.FileHandler(file_name)
          formatter = logging.Formatter('%(message)s')
          file_handler.setFormatter(formatter)
          logger.addHandler(file_handler)
          logger.addHandler(stream_handler)
          logger.setLevel(logging.INFO)
          logger.propagate = False
          logger.handler_set = Truereturn logger

--- modc.py ---

  import mylogger

  def writelog():
      print("Hello from " + __name__)
      print(__name__, 'LogID:', id(mylogger.setLogger()))
      mylogger.setLogger().warning("Hello from " + __name__)

--- modb.py ---

  import mylogger
  import modc

  def writelog():
      print("Hello from " + __name__)
      print(__name__, 'LogID:', id(mylogger.setLogger()))
      mylogger.setLogger().warning("Hello from " + __name__)

  modc.writelog()

--- moda.py ---

  import mylogger

  def writelog():
      print("Hello from " + __name__)
      print(__name__, 'LogID:', id(mylogger.setLogger()))
      mylogger.setLogger().warning("Hello from " + __name__)
      
  import modb
  import modc

  writelog()
  modb.writelog()
  modc.writelog()

I ran moda.py. Here is the output. The logger is created once and every module uses the same instance of the logger. All messages are saved to the same file. Note that I'm using python 3.7.

  Hello from modc
  Creating logger
  modc LogID: 1764613056456
  Hello from modc
  Hello from __main__
  __main__ LogID: 1764613056456
  Hello from __main__
  Hello from modb
  modb LogID: 1764613056456
  Hello from modb
  Hello from modc
  modc LogID: 1764613056456
  Hello from modc