@Marvin how can I produce log output from a deployed flow?

To help you with logging output from a deployed flow, I need to know which version of Prefect you're using. Can you please confirm whether you're using Prefect 2.x, or have you already taken the leap into the world of Prefect 3.x? If you’re unsure, any detail about your setup could help.

@Marvin it's Prefect 3.x

To produce log output from a deployed flow in Prefect 3.x, you can use Prefect's built-in logging capabilities. Here’s how you can do it: 1. Automatic Logging: Prefect automatically logs key events during the execution of flows and tasks. These logs include state changes, error tracebacks, and other lifecycle events. You can view these logs in the Prefect UI, CLI, or through the API. 2. Custom Logging: For more specific log messages, you can emit custom logs by using Prefect's loggers: - Import the logger:

python
     from prefect.logging import get_run_logger

- Use the logger within your flow or task to log messages that are relevant to your application's events or state:

python
     logger = get_run_logger()
     <http://logger.info|logger.info>("This is an informational message")

3. Configuration: Prefect logging can be configured in several ways: - Set environment variables such as

PREFECT_LOGGING_ROOT_LEVEL

to adjust the logging level. - Customize logging with a configuration file

logging.yml

placed in your

PREFECT_HOME

directory, if more advanced configuration is needed. For additional information on logging configurations, you may refer to the Prefect 3.x logging documentation. With these tools at your disposal, you can ensure that your flow's logs are as informative and detailed as a digital version of Vogon poetry (but hopefully less painful to read).

@Marvin can I format the Log message to include the value of a python variable

Absolutely! In Prefect, you can format log messages to include the value of a Python variable. You can do this by using Python's f-string syntax, which allows you to embed expressions inside string literals to be evaluated at runtime. Here’s an example:

python
from prefect import flow
from prefect.logging import get_run_logger

@flow
def my_flow():
    logger = get_run_logger()
    my_variable = 42
    <http://logger.info|logger.info>(f"The value of my_variable is: {my_variable}")

my_flow()

In this example, the log message will include the current value of

my_variable

. You can, of course, include any other variables or expressions in a similar way. It's like a dynamic template for your logs, without needing to resort to old-school format strings or concatenation—even though those techniques are still around, lurking, much like my existential dread. For more details, you can check Prefect's logging documentation here: Prefect 3.x logging.