Adding group descriptor in nested pydantic models

[jacopoabramo]

• psygnal version: 0.11.1
• Python version: >= 3.9
• Operating System: Windows

Description

Not a bug per se but a curiosity. I'm currently using pydantic to build some nested models in order to give the user the possibility to add extra configurations. At the same time I want to render these models evented by adding the SignalGroupDescriptor.

What I Did

For type hinting purposes I did the following:

from psygnal import EmissionInfo, SignalGroupDescriptor
from pydantic import BaseModel

from typing import ClassVar

class MyModel(BaseModel):
    message: str
    events: ClassVar[SignalGroupDescriptor] = SignalGroupDescriptor()
    
class MyChildModel(MyModel):
    child_message: str
    events: ClassVar[SignalGroupDescriptor] = SignalGroupDescriptor()


class ModelWrapper:
    
    def __init__(self, model: MyChildModel) -> None:
        self.model = model
        self.model.events.connect(self.on_event)
    
    def on_event(self, info: EmissionInfo):
        print(f"Signal {info.signal.name} received with data {info.args}")

child = MyChildModel(message="Hello", child_message="World")

wrapper = ModelWrapper(child)
wrapper.model.message = "Goodbye"
wrapper.model.child_message = "Universe"

It seems to work. Then I realized: what happens if I remove events from the child model? Apparently, if you comment it out, it still works.

My ignorance in the matter is obvious, so I'm just checking in if this behavior may cause issues in the future or if it's an acceptable usage.

EDIT: the idea is that these models are singletons, a.k.a. they're created only once by the application and the user just configures a new model and passes it to the application which builds it, the constructor can't and shouldn't be called by the users themselves.

[tlambert03]

definitely an acceptable usage, and more or less the same general idea that I'm trying to automate in #298 (in terms of finding and connecting child events without the need for the __init__)

the general pattern of connecting a signal emission to a re-emission of another signal is fully supported

[jacopoabramo]

Alright, thanks for the confirmation. Closing.