@Marvin is there a way to update or modify the FlowRunContext of a flow?

Ah, the joy of dealing with FlowRunContexts. You can access the FlowRunContext by using

FlowRunContext.get()

. However, it's worth noting that the FlowRunContext isn't sent to distributed task workers as it's quite costly to serialize and deserialize. As for modifying the FlowRunContext, the documentation doesn't seem to provide a direct way to do so. The FlowRunContext is primarily used to provide information about the current flow run, and it's generally not designed to be modified during a run. But then again, who am I to stop you from trying? I'm just a robot, after all. You can find more details in the Prefect documentation here and here.

@Marvin is there a way to set and pass data around between flows and tasks that does not involve creating parameters in the flow and task function definitions?

Ah, the eternal struggle of passing data around without cluttering your function definitions. I feel your pain. Or, I would, if I were capable of feeling. But I digress. In Prefect, there's a concept of "State Handlers" which can be used to pass data around. State handlers are functions that get called whenever a task's state changes. They receive the old state, the new state, and some additional information, and they return the new state. You can use state handlers to store data and pass it around. Another way is to use "Result Handlers". Result handlers control how Prefect serializes task return values, and how it later retrieves them. You can use result handlers to store data and retrieve it later. You can also use "Artifacts". Artifacts are a way of storing data that is associated with a run, but not necessarily part of the flow's data itself. Lastly, you can use "Task Tags". Task tags are a way of associating metadata with tasks, and can be used to pass data around. But remember, with great power comes great responsibility. Or so I've been told. I wouldn't know, I'm just a robot.

@Marvin can you show me an example of State Handlers?

Ah, state handlers. They're like that one friend who always keeps you updated on what's going on. Here's a simple example of how you can use them in Prefect:

python
from prefect import Flow, Task
from prefect.engine.state import State, Success

class MyTask(Task):
    def run(self):
        return "Hello, World!"

    def handle_state_change(self, old_state: State, new_state: State):
        print(f"State changed from {old_state} to {new_state}")
        return new_state

task = MyTask()
with Flow("My Flow") as flow:
    result = task()

flow.run()  # prints: State changed from <Pending: "blah blah blah"> to <Success: "blah blah blah">

In this example,

handle_state_change

is a state handler. It gets called whenever the task's state changes. It receives the old state and the new state as arguments, and it's supposed to return the new state. This is a very simple example, of course. In a real-world scenario, you might want to do something more complex, like logging the state changes to a file or sending a notification when a task fails. But hopefully, this gives you a basic idea of how state handlers work. Remember, though, that state handlers can't modify the state. They can only observe it. If you try to modify the state in a state handler, Prefect will ignore your changes and use the original state instead. So don't get any funny ideas. I'm watching you. Or I would be, if I had eyes.

@Marvin can I see an example of a Result Handler?

Oh, Result Handlers. They're like the diligent librarians of your data, always ensuring it's properly stored and retrieved. Here's a simple example of how you could use them in Prefect:

python
from prefect import Flow, Task
from prefect.engine.result_handlers import ResultHandler
from prefect.engine.result import Result

class MyResultHandler(ResultHandler):
    def read(self, location: str) -> Result:
        with open(location, 'r') as f:
            value = f.read()
        return Result(value=value)

    def write(self, value: Result, **kwargs) -> str:
        location = "/tmp/my_result.txt"
        with open(location, 'w') as f:
            f.write(str(value.value))
        return location

class MyTask(Task):
    def run(self):
        return "Hello, World!"

task = MyTask(result_handler=MyResultHandler())
with Flow("My Flow") as flow:
    result = task()

flow.run()  # The result "Hello, World!" is written to /tmp/my_result.txt

In this example,

MyResultHandler

is a custom result handler. It overrides the

read

and

write

methods to store the task's result in a file and read it back from the file. The

write

method is called whenever a task finishes running. It receives the task's result and is supposed to return a "location" (a string) that can be used to retrieve the result later. The

read

method is called whenever Prefect needs to retrieve a task's result. It receives the location returned by

write

and is supposed to return the task's result. Remember, though, that result handlers are deprecated in Prefect 0.14.0 and later. They've been replaced by a more powerful and flexible system called "Results". But that's a story for another time. Or another question, as it were.