In Python how to pass a common object to different module files

Question 1

I have various module files and want to share a common object (in this case a logger) to each of them. What is the best way to do this? I have a solution but it does not feel just right.

In pseudo code:

module_1.py

global logger
# module_1
def pass_logger_module1(plogger):
 global logger
 logger = plogger

module_2.py

global logger
# module_2
def pass_logger_module2(plogger):
 global logger
 logger = plogger

main_module.py

from module_1 import pass_logger_module1
from module_2 import pass_logger_module2
logger = set_logger(logfile, logformat, 'DEBUG')
pass_logger_module1(logger)
pass_logger_module2(logger)

Question 2

That isn't how you should be using loggers. The logging module has the specific ability to define a parent logger with the settings you want and for child loggers to inherit them. You should read the documentation.

Question 3

Thanks I will do. However in more general terms what is the best way to share a common object?

Question 4

The best way is to pass it explicitly to each function that needs it and/or save it in objects that use it.

Question 5

As pointed out in the comments this isn't the way use the logging module.

however a more general answer for "common object to different module files" is to do it the other way around from your example, meaning:

main_module.py

# this is in global
logger = set_logger(logfile, logformat, 'DEBUG')

module_1.py

from main_module import logger

module_2.py

from main_module import logger

EDIT: to avoid making a circular import perhaps store the logger in a different module:

settings.py

# this is in global
logger = set_logger(logfile, logformat, 'DEBUG')

main_module.py

from settings import logger

Question 6

this gives me circular import situation, but as suggested I can put the shared object in yet another module file and import from there...

Question 7

Thanks that worked well. I had a setup module, however each module initiated its own instance of this setup, which worked ok for object that do not change in value, however I had my logger initiated several times. I have to rewrite it to make the setup object class objects and not instance objects...

Question 8

It won't, You will get the same module that has already been imported (it will come from sys.modules). I encourage you check for yourself to see that it's true!

Question 9

One way to do this is to expose your shared object through a third module, like so:

my_logger.py

logger = set_logger(logfile, logformat, 'DEBUG')

module_1.py

from my_logger import logger
...

module_2.py

from my_logger import logger
...

Your main module can then import both module_1 and module_2 without knowing about the logger and avoiding a circular import situation.

Question 10

First, define your custom logger in custom_logger.py

import logging
import sys
class CustomFormatter(logging.Formatter):
 err_fmt = "[*] ERROR: %(msg)s"
 dbg_fmt = "[-] DEBUG: %(module)s: %(lineno)d: %(msg)s"
 info_fmt = "[+] %(msg)s"
 def __init__(self):
 super().__init__(fmt="%(levelno)d: %(msg)s", datefmt=None, style='%')
 def format(self, record):
 # Save the original format configured by the user
 # when the logger formatter was instantiated
 format_orig = self._style._fmt
 # Replace the original format with one customized by logging level
 if record.levelno == logging.DEBUG:
 self._style._fmt = CustomFormatter.dbg_fmt
 elif record.levelno == logging.INFO:
 self._style._fmt = CustomFormatter.info_fmt
 elif record.levelno == logging.ERROR:
 self._style._fmt = CustomFormatter.err_fmt
 # Call the original formatter class to do the grunt work
 result = logging.Formatter.format(self, record)
 # Restore the original format configured by the user
 self._style._fmt = format_orig
 return result
class CustomLogger(logging.Logger):
 def __init__(self, *args, **kwargs):
 super().__init__(*args, **kwargs)
 formatter = CustomFormatter()
 handler = logging.StreamHandler(sys.stdout)
 handler.setFormatter(formatter)
 self.addHandler(handler)
 self.setLevel(logging.INFO)

Then, in your other modules, import CustomLogger.

from custom_logger import CustomLogger
logger = CustomLogger(__name__)
logger.debug("Hello, world!")

moshevi 6,2916 gold badges40 silver badges57 bronze badges · Accepted Answer · 2018-07-19 13:48:54Z

2

As pointed out in the comments this isn't the way use the logging module.

however a more general answer for "common object to different module files" is to do it the other way around from your example, meaning:

main_module.py

# this is in global
logger = set_logger(logfile, logformat, 'DEBUG')

module_1.py

from main_module import logger

module_2.py

from main_module import logger

EDIT: to avoid making a circular import perhaps store the logger in a different module:

settings.py

# this is in global
logger = set_logger(logfile, logformat, 'DEBUG')

main_module.py

from settings import logger

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edited Jul 21, 2019 at 23:29

answered Jul 19, 2018 at 13:48

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moshevi

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3 Comments

Bruno Vermeulen

Bruno Vermeulen Over a year ago

this gives me circular import situation, but as suggested I can put the shared object in yet another module file and import from there...

2018年07月19日T14:07:45.147Z+00:00

Bruno Vermeulen

Bruno Vermeulen Over a year ago

Thanks that worked well. I had a setup module, however each module initiated its own instance of this setup, which worked ok for object that do not change in value, however I had my logger initiated several times. I have to rewrite it to make the setup object class objects and not instance objects...

2018年07月19日T15:19:32.603Z+00:00

moshevi

moshevi Over a year ago

It won't, You will get the same module that has already been imported (it will come from sys.modules). I encourage you check for yourself to see that it's true!

2018年07月22日T06:47:34.573Z+00:00

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