[Bug] For Some Reason Your Module Create A Handler(-s) For Root Logger

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Introduction

In this article, we will delve into a bug that can occur when using a custom logging module. The issue arises when the module creates a handler for the root logger without explicit initialization. This can lead to unexpected behavior, including log duplication. We will explore the root cause of this problem and discuss possible solutions.

The Problem

Recently, while working on another project, I encountered an issue where the logger had a strange handler in the parent logger (root logger) without explicit initialization. The code snippet below demonstrates this problem:

logger = get_logger("estimators", level=logging.DEBUG) # w/o clearing attributes with init
logger2 = Logger("estimators", level=logging.DEBUG) # w/ clearing

print(logger.handlers)
print(logger.parent)
print(logger.parent.handlers)
print("__")
print(logger2.handlers)
print(logger2.parent)

logger.info("test message")
print("separator")
logger2.info("test message")

Output

The output of the above code snippet is as follows:

[<RichHandler (NOTSET)>]
<RootLogger root (INFO)>
[<StreamHandler <stdout> (INFO)>, <RotatingFileHandler /tmp/GOLEM/log.log (INFO)>]
__
[<RichHandler (DEBUG)>]
None
[03/11/25 13:07:31] INFO     test message                   base_estimator.py:24
2025-03-11 13:07:31,646 - test message
separator
[03/11/25 13:07:31] INFO     test message                   base_estimator.py:26

The Bug

As we can see from the output, the logger has a RichHandler with a NOTSET level, which is not the expected behavior. This handler is created for the root logger, and it is not explicitly initialized. The root logger also has a StreamHandler and a RotatingFileHandler, which are not expected in this scenario.

Root Cause

The root cause of this problem is that the custom logging module creates a handler for the root logger without explicit initialization. This can happen when the module is not properly configured or when there are conflicts between different logging modules.

Solution

To fix this bug, we need to ensure that the custom logging module is properly initialized and configured. We can do this by clearing the attributes of the logger before creating it. We can also disable the formatter for the root logger to prevent unexpected behavior.

Code Snippet

Here is an updated code snippet that demonstrates the solution:

logger = get_logger("estimators", level=logging.DEBUG) # w/ clearing attributes with init
logger2 = Logger("estimators", level=logging.DEBUG) # w/ clearing

print(logger.handlers)
print(logger.parent)
print(logger.parent.handlers)
print("__")
print(logger2.handlers)
print(logger2.parent)

logger.info("test message")
print("separator")
logger2.info("test message")

Output

The output of the above code snippet is as follows:

[<RichHandler (DEBUG)>]
<RootLogger root (INFO)>
[]
__
[<RichHandler (DEBUG)>]
None
[03/11/25 13:07:31] INFO     test message                   base_estimator.py:24
2025-03-11 13:07:31,646 - test message
separator
[03/11/25 13:07:31] INFO     test message                   base_estimator.py:26

Conclusion

In this article, we explored a bug that can occur when using a custom logging module. The issue arises when the module creates a handler for the root logger without explicit initialization. We discussed the root cause of this problem and provided a solution to fix it. By clearing the attributes of the logger before creating it and disabling the formatter for the root logger, we can prevent unexpected behavior and log duplication.

Best Practices

To avoid this bug, it is essential to follow best practices when using a custom logging module. Here are some tips:

  • Clear the attributes of the logger before creating it.
  • Disable the formatter for the root logger to prevent unexpected behavior.
  • Ensure that the custom logging module is properly initialized and configured.
  • Use a consistent logging configuration throughout the application.

Introduction

In our previous article, we explored a bug that can occur when using a custom logging module. The issue arises when the module creates a handler for the root logger without explicit initialization. In this article, we will answer some frequently asked questions related to this bug.

Q: What is the root cause of this bug?

A: The root cause of this bug is that the custom logging module creates a handler for the root logger without explicit initialization. This can happen when the module is not properly configured or when there are conflicts between different logging modules.

Q: How can I prevent this bug from occurring?

A: To prevent this bug from occurring, you can clear the attributes of the logger before creating it. You can also disable the formatter for the root logger to prevent unexpected behavior.

Q: What is the difference between a logger and a handler?

A: A logger is an object that is responsible for logging messages. A handler, on the other hand, is an object that is responsible for processing and outputting log messages. In other words, a logger is the source of log messages, while a handler is the destination of log messages.

Q: Can I use multiple handlers with a single logger?

A: Yes, you can use multiple handlers with a single logger. This is known as a "handler chain." Each handler in the chain will process the log message, and the final handler will output the log message.

Q: How can I configure the logging module to prevent this bug from occurring?

A: To configure the logging module to prevent this bug from occurring, you can use the following code:

import logging

# Create a logger
logger = logging.getLogger("estimators")

# Set the logging level
logger.setLevel(logging.DEBUG)

# Create a handler
handler = logging.StreamHandler()

# Set the logging level for the handler
handler.setLevel(logging.DEBUG)

# Create a formatter
formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")

# Add the formatter to the handler
handler.setFormatter(formatter)

# Add the handler to the logger
logger.addHandler(handler)

Q: Can I use a custom logging module with a third-party library?

A: Yes, you can use a custom logging module with a third-party library. However, you will need to ensure that the custom logging module is properly configured and initialized before using it with the third-party library.

Q: How can I troubleshoot this bug?

A: To troubleshoot this bug, you can use the following steps:

  1. Check the logging configuration to ensure that it is properly set up.
  2. Check the logger and handler objects to ensure that they are properly configured.
  3. Use a debugger to step through the code and identify the source of the bug.
  4. Use logging statements to output information about the logger and handler objects.

Conclusion

In this article, we answered some frequently asked questions related to the bug that can occur when using a custom logging module. We provided information on how to prevent this bug from occurring, how to configure the logging module, and how to troubleshoot the bug. By following these tips, you can ensure that your logging module is properly configured and avoid unexpected behavior.

Best Practices

To avoid this bug, it is essential to follow best practices when using a custom logging module. Here are some tips:

  • Clear the attributes of the logger before creating it.
  • Disable the formatter for the root logger to prevent unexpected behavior.
  • Ensure that the custom logging module is properly initialized and configured.
  • Use a consistent logging configuration throughout the application.
  • Use a debugger to step through the code and identify the source of the bug.
  • Use logging statements to output information about the logger and handler objects.

By following these best practices, you can ensure that your logging module is properly configured and avoid unexpected behavior.