How to Log to Both File and Console in Python Using logging.StreamHandler?

Logging to Both File and Console in Python

Python logging provides robust functionality for message handling. By default, messages are typically written to a designated log file. However, you may also wish to duplicate these messages to the console, ensuring immediate visibility during program execution.

To achieve this, utilize the logging.StreamHandler class, which allows you to write logging output to sys.stdout, the standard output stream. Follow these steps:

1. Import the logging module: Begin by importing the logging module into your script.
2. Configure a StreamHandler: Create an instance of logging.StreamHandler and specify the output stream destination, such as sys.stdout for console output. You can also set the handler's level to filter the messages it processes.
3. Set the formatter: Define a logging.Formatter object to format the output messages. You can specify the desired format string to customize the message layout.
4. Attach the handler to the root logger: Add the configured StreamHandler to the root logger to enable logging messages to both the log file and the console. This involves setting its level and adding the handler.

Here's an example of how to configure a StreamHandler:

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

# Create a StreamHandler using sys.stdout
handler = logging.StreamHandler(sys.stdout)
handler.setLevel(logging.DEBUG)

# Define a formatter and set it on the handler
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
handler.setFormatter(formatter)

# Add the handler to the root logger
root = logging.getLogger()
root.addHandler(handler)</code>

By implementing these steps, you can conveniently output all logging messages to both the log file and the console, providing a comprehensive view of your application's logging activity.

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