@Marvin how do I fix the following error where a custom block type is used to create a block:

"No class found for dispatch key 'secure-generic-credentials' in registry for type 'Block'."

It appears there's a problem with Prefect recognizing your custom block type. Here are the potential solutions: 1. Ensure the Custom Block is Registered Properly: When creating a custom block, you need to ensure it is registered correctly. Define a class that subclasses

Block

and register the block appropriately. 2. Documentation on Creating and Using Blocks: The process of creating and registering custom blocks is outlined in the Prefect documentation. You can follow the instructions here to properly declare and register your custom block. To help you further, please provide more details on how you're creating and using your custom block. If you've already followed the documentation and still face issues, verifying the block's registration or checking for typos in the dispatch key might be necessary. For more in-depth guidance, refer to the provided documentation link.

@Marvin, I have created my own custom block type and registered it. I can see the block type is registered by using

prefect block type ls

. I created a block from the custom block type using the Prefect Cloud UI. I can see that the block is registered when I run

prefect block ls

. I am getting an error when loading the block in my code. The code I am using is:

from prefect.blocks.core import Block
some_creds = Block.load("generic-credentials/some-usage-of-creds")

When I execute the code I am presented with this error:

KeyError: "No class found for dispatch key 'generic-credentials' in registry for type 'Block'."

How can I fix this error?

It appears that while you've registered your custom block type successfully, the issue might be stemming from the block's class not being imported or registered correctly when you run your script. Here are a few steps and solutions you can try: 1. Ensure Proper Import of the Custom Block Class: Make sure the custom block class is imported in the script before you try to load it. For example:

python
   from your_custom_module import GenericCredentials
   from prefect.blocks.core import Block
   
   some_creds = Block.load("generic-credentials/some-usage-of-creds")

2. Check the Naming and Registration: Verify that the name used in

Block.load

matches exactly with the registered block type, including case sensitivity. 3. Re-register the Block Type: Ensure that the block type is registered in the current Python environment where you are running your script:

python
   from prefect.blocks.core import Block
   from your_custom_module import GenericCredentials
   
   GenericCredentials.register_type()
   some_creds = Block.load("generic-credentials/some-usage-of-creds")

4. Manual Loading Using Custom Class: Instead of using

Block.load

, you can directly use the class name to load the block:

python
   from your_custom_module import GenericCredentials
   
   some_creds = GenericCredentials.load("generic-credentials/some-usage-of-creds")

To see a detailed guide on creating, registering, and using custom block types, refer to the Prefect documentation here. Give these steps a try and let me know if you still face issues.

@Bryan the custom block class you wrote still needs to be present and imported wherever you're trying to load an instance of it

yep kevin beat me here, i would call MyBlockClass.load(name) instead of Block.load(type/name)

Ok. I am wondering how this works if someone else wants to use the Block Type created in various other Prefect projects. Is there not a generic way to access the blocks from other locations or do those locations also need to have the class defined in those projects as well?

the class needs to be defined everywhere you use it

generally speaking, if you’re planning on sharing your block type, I would package it into a module that can be pip installed by someone else in your org, so they can import the type cleanly

you could release it as a package hosted on a private registry and install where needed, install it from git where needed, or just copy the class definition module to every project you use it in

One more question. What does registering the block type do if it can't be reused without the class?

it tells Prefect the structure of the data and data types that need to be stored so block instances can be translated between your code and our storage backend while providing a nice UI for editing the contents outside the code if needed

that's correct. it tells the server the shape of your block so UI and friends know how to render and treat it, which is entirely separate from your python environment clientside if you want to start a library of utils (functions, blocks, etc) that you can share with your team, there's a template here

It sounds like a feature request to have a generic block type baked into prefect to store something like a simple username and password where both attributes are SecureStr's. Is that accurate? If so, where do I officially do that?

I think a reasonable request would be a block type like

SecretDict

which stores a

value: Dict[str, SecretStr]

or something like that you can open an issue here if that sounds like what you need

I like the the request suggestion @Nate. I will post something out there. Thanks to both of you.