How Can I Automatically Log Uncaught Exceptions in Python?

Logging Uncaught Exceptions in Python

Catching and handling exceptions is crucial for error handling in Python. However, what about uncaught exceptions that would otherwise be printed to the standard error output (stderr)?

Custom Exception Handling

While it's always advisable to catch and handle exceptions explicitly, sometimes it can be convenient to automate the logging of uncaught exceptions. Instead of relying on a try/except block, the following solution allows for logging to occur automatically:

<code class="python">import sys
import logging

# Create a custom exception handler
def handle_exception(exc_type, exc_value, exc_traceback):
    if issubclass(exc_type, KeyboardInterrupt):
        sys.__excepthook__(exc_type, exc_value, exc_traceback)
        return

    # Use the logging module to handle the uncaught exception
    logger = logging.getLogger(__name__)
    logger.error("Uncaught exception", exc_info=(exc_type, exc_value, exc_traceback))

# Replace the default exception handler with our custom one
sys.excepthook = handle_exception

# Set up a logger and handler
logger = logging.getLogger(__name__)
handler = logging.StreamHandler(stream=sys.stdout)
logger.addHandler(handler)

# Raise an exception to test the custom exception handling
if __name__ == "__main__":
    raise RuntimeError("Test unhandled")</code>

Explanation

This code accomplishes several tasks:

• Creates a custom exception handler function (handle_exception) that takes standard exception parameters (exc_type, exc_value, and exc_traceback).
• Within handle_exception, the code ignores KeyboardInterrupt exceptions (so you can use Ctrl C to exit the program normally).
• Uncaught exceptions are logged using the logging module, with a custom message "Uncaught exception" and the exception details.
• The custom exception handler is registered as the default exception handler, replacing Python's default behavior of printing to stderr.

By automating the logging of uncaught exceptions, this approach simplifies error handling and provides a central location to review all exceptions that occur during program execution, whether they are caught or not.

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