Getting Started with Logging in DUNE-DAQ

By the end of this tutorial you will have a working logger printing colour-formatted output to your terminal. It should take about five minutes. No prior knowledge of Python logging is assumed — if you want to understand the concepts behind what you're doing, read Concepts & explanation afterwards.

Prerequisites

Before starting, make sure you have:

The DUNE DAQ environment loaded (i.e. dbt-setup-env or equivalent has been run in your shell)
daqpytools installed in your environment

Step 1: Initialize a logger

Initializing a logger instance is simple:

from daqpytools.logging import get_daq_logger
test_logger = get_daq_logger(
    logger_name = "test_logger", # Set as your logger name. Preferrably it should be relevant to what module / file you are in 
    log_level = "INFO", # Default level you will transmit at or above. In this case, Debugs will not be transmitted
    use_parent_handlers = True, # Just keep this true

    ## the rest are whatever handlers you want to attach. Read on for what exists. Rich is your standard TTY logger so the vast majority will be using this
    rich_handler = True, 
    stream_handlers = False # you dont really need this; its False by default
)

Please see the API reference of get_daq_logger here, or alternatively the code itself here, to see what options exist in initialising get_daq_logger.

This gives you a named logger with a single Rich handler attached, emitting at INFO level and above. Loggers in daqpytools are singletons — calling get_daq_logger with the same name twice will return the same instance, so it's safe to call this once at module level and reuse it throughout your code.

Step 2: Emit your first messages

Emitting refers to the act of processing the log record and sending it out to its intended destination! You can emit your messages to the terminal, to a file, via a RESTapi, and so on. For this tutorial, we are simply emitting a message to the terminal.

test_logger.info("Hello, world!")

test_logger.info(
        "[dim cyan]Look[/dim cyan] "
        "[bold green]at[/bold green] "
        "[bold yellow]all[/bold yellow] "
        "[bold red]the[/bold red] "
        "[bold white on red]colours![/bold white on red] "
)

You should see colour-formatted output in your terminal, something like this:

rich_demo

The Rich handler supports the full Rich markup syntax inline in your log messages.

Next steps

To explore the full range of available handlers and filters interactively, run the logging demonstrator with the DUNE environments loaded:
```
daqpytools-logging-demonstrator
```
View the help string to learn more, and the script itself in the repository to see how it is implemented.
To understand why logging works the way it does, read the Concepts & explanation.
To learn how to use specific handlers and filters, see the How-to guides.
For a full API reference, see the API Reference.
If you are introducing logging to your Python repo, or upgrading an existing implementation, please read the Logging best practices.