@Marvin How to register a custom block with custom functions in the block? I also want those functions to be presented in the UI as tasks

To register a custom block with custom functions in Prefect 3.x and have those functions presented in the UI as tasks, you'll need to follow these steps: 1. Create a Custom Block: - Define a class that subclasses

Block

. This class will represent your custom block. The

Block

base class builds on Pydantic's

BaseModel

, allowing you to declare custom fields. 2. Register the Custom Block: - You can register the block using the CLI command

prefect block register

. If your custom block is defined in a Python module, you can register all blocks found within that module using this command. 3. Define Functions as Tasks: - To have functions within the block presented as tasks in the UI, you can define these functions using the

@task

decorator from Prefect. This decorator allows Prefect to recognize these functions as tasks that can be orchestrated within a flow. 4. Linking to the UI: - Once the tasks are defined, they will automatically appear in the Prefect UI when you create a flow that includes these tasks. For more detailed guidance, you can refer to the Prefect documentation on creating and registering blocks here. If you need to explore the Prefect API further, you can check the top-level API offerings, such as

flow

,

task

, and other utilities.

@Marvin Could you provide me with a simple example?

Here's a simple example of how you might define a custom block with functions presented as tasks in Prefect 3.x:

python
from prefect import task, flow
from prefect.blocks.core import Block

# Define a custom block by subclassing Block
class MyCustomBlock(Block):
    # Add any custom fields or methods here
    name: str

    @task
    def greet(self):
        print(f"Hello from {self.name}!")

# Register the block using the CLI:
# Run this command in your terminal after saving this script:
# prefect block register -m your_module_name

# Example flow using the custom block
@flow
def my_flow():
    block = MyCustomBlock(name="CustomBlockExample")
    block.greet()  # This will be presented as a task in the UI

# Execute the flow
if __name__ == "__main__":
    my_flow()

### Steps to Follow: 1. Define the Block: Create a class inheriting from

Block

and define any custom fields or methods. Use the

@task

decorator for methods you want to present as tasks. 2. Register the Block: Use the CLI command

prefect block register -m your_module_name

to register your block. Replace

your_module_name

with the name of the module where your block is defined. 3. Create a Flow: Define a flow that uses your custom block and calls its methods. The methods decorated with

@task

will appear as tasks in the Prefect UI. For more information on blocks, you can visit the Prefect documentation on blocks.

@Marvin This results in an error: pydantic.errors.PydanticUserError: A non-annotated attribute was detected:

greet = <prefect.tasks.Task object at 0x104e0cf40>

. All model fields require a type annotation; if

greet

is not meant to be a field, you may be able to resolve this error by annotating it as a

ClassVar

or updating

model_config['ignored_types']

.

The error you're encountering is due to Pydantic's requirement that all attributes in a model (like

Block

) must have type annotations. Since

@task

creates a Prefect task object, it needs to be handled differently. Here's how you can modify the example to resolve this error: 1. Define the task outside the block class. 2. Use the block's data within the task. Here's the updated example:

python
from prefect import task, flow
from prefect.blocks.core import Block

# Define a custom block by subclassing Block
class MyCustomBlock(Block):
    name: str

# Define the task separately
@task
def greet(block: MyCustomBlock):
    print(f"Hello from {block.name}!")

# Example flow using the custom block
@flow
def my_flow():
    block = MyCustomBlock(name="CustomBlockExample")
    greet(block)  # Pass the block to the task

# Execute the flow
if __name__ == "__main__":
    my_flow()

### Key Adjustments: - Task Definition: Define the

greet

task outside of the

MyCustomBlock

class. - Task Execution: Pass the block instance to the task function as a parameter. This approach keeps the

Block

class clean and ensures that the task is correctly recognized and executed by Prefect.