# Python Logging Module

The `logging` module defines functions and classes which implement a flexible event logging system for applications and libraries. It is superior to using `print()` statements because it allows you to categorize messages by severity and direct them to different outputs (console, files, etc.).

## Importing the Module

```python
import logging
```

## Basic Configuration

The simplest way to configure logging is using `basicConfig`.

```python
import logging

# Configure logging to show messages of level INFO and higher
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')

logging.debug("This is a debug message")      # Won't show (level < INFO)
logging.info("This is an info message")       # Will show
logging.warning("This is a warning message")  # Will show
logging.error("This is an error message")     # Will show
logging.critical("This is a critical message")# Will show
```

## Logging Levels

| Level | Numeric Value | Description |
| :--- | :--- | :--- |
| `DEBUG` | 10 | Detailed information, typically of interest only when diagnosing problems. |
| `INFO` | 20 | Confirmation that things are working as expected. |
| `WARNING` | 30 | An indication that something unexpected happened, or indicative of some problem in the near future (e.g. 'disk space low'). |
| `ERROR` | 40 | Due to a more serious problem, the software has not been able to perform some function. |
| `CRITICAL` | 50 | A serious error, indicating that the program itself may be unable to continue running. |

## Logging to a File

You can direct logs to a file by specifying the `filename` argument in `basicConfig`.

```python
logging.basicConfig(filename='app.log', level=logging.DEBUG)
logging.info("Started application")
```

## Advanced Usage (Loggers)

For larger applications, avoid using the root logger directly. Create a named logger.

```python
logger = logging.getLogger(__name__)
logger.info("Message from specific module")
```

[[programming/python/python]]