Python neither logging to console nor to file

Question

I have following code in my colab notebook:

# Cell 1
import logging


# Cell 2
class MyClass:
  def __init__(self):
    self.configureLogger()
    self.fileLogger.info('info log to file')
    self.consoleLogger.debug('debug log to console')    

  def configureLogger(self):
    # https://stackoverflow.com/a/56144390/6357916
    # logging.basicConfig(level=logging.NOTSET)
    self.fileLogger = logging.getLogger('fileLogger2')
    if not self.fileLogger.hasHandlers():
        self.fileLogger.setLevel(logging.INFO)
        formatter1 = logging.Formatter("%(asctime)s,%(message)s")
        file_handler = logging.FileHandler('log.txt')
        file_handler.setLevel(logging.INFO)
        file_handler.setFormatter(formatter1)
        self.fileLogger.addHandler(file_handler)

    self.consoleLogger = logging.getLogger('consoleLogger2')
    if not self.consoleLogger.hasHandlers():
        self.consoleLogger.setLevel(logging.DEBUG)
        formatter2 = logging.Formatter("%(message)s")
        console_handler = logging.StreamHandler()
        console_handler.setFormatter(formatter2)
        self.consoleLogger.addHandler(console_handler)

c = MyClass()

There MyClass has a method called configureLogger() which configures two loggers:

1. fileLogger: logs to file
2. consoleLogger: logs t console

MyClass.__init__() call this method and uses both of these loggers to log single message each. But nothing gets logged to console. Nor does log.txt file gets created.

I am expecting it to log debug log to console to console and info log to file to file. This is how it is behaving on my local machine, but fails on colab

What I am missing here?

Update

After commenting both line containing if ..., it is now printing

2023-04-07 20:10:20,860,info log to file

to file and

INFO:fileLogger2:info log to file
debug log to console
DEBUG:consoleLogger2:debug log to console

to console.

It means those if conditions are false causing no file handler are getting added and that is why nothing was getting logged. But those if conditions should be true initially right (as logger should not have any handler to start with)?

Answer 1

The logger names fileLogger2 and consoleLogger2 are both children of the root logger, which has the default level set to WARNING. This means that the messages with lower log levels (like INFO and DEBUG) will not propagate to the root logger and won't be logged. You can set the propagate attribute of your loggers to False, which would prevent the messages from being passed to the parent loggers allowing you to see the log messages as expected:

def configureLogger(self):
    self.fileLogger = logging.getLogger('fileLogger2')
    if not self.fileLogger.hasHandlers():
        self.fileLogger.setLevel(logging.INFO)
        self.fileLogger.propagate = False  # Add this line
        formatter1 = logging.Formatter("%(asctime)s,%(message)s")
        file_handler = logging.FileHandler('log.txt')
        file_handler.setLevel(logging.INFO)
        file_handler.setFormatter(formatter1)
        self.fileLogger.addHandler(file_handler)

    self.consoleLogger = logging.getLogger('consoleLogger2')
    if not self.consoleLogger.hasHandlers():
        self.consoleLogger.setLevel(logging.DEBUG)
        self.consoleLogger.propagate = False  # Add this line
        formatter2 = logging.Formatter("%(message)s")
        console_handler = logging.StreamHandler()
        console_handler.setFormatter(formatter2)
        self.consoleLogger.addHandler(console_handler)

https://docs.python.org/3/library/logging.html#logging.Logger.propagate

---

EDIT: Alternatively, you can remove existing handlers by adding logging.root.handlers.clear() to your configureLogger() method. Also, because we remove any existing handlers we do not need to care any propagation (as there is nothing to propagate to), so remove self.consoleLogger.propagate = False line I suggested previously:

def configureLogger(self):
    logging.root.handlers.clear()  # Add this line

    ...
    self.consoleLogger.propagate = False  # Remove this (x2)
    ...