Incorrect pydantic example in Python SDK docs

[damianr13]

In the python SDK docs we have the following code snippet:

class Delivery(BaseModel):
    timestamp: datetime
    dimensions: tuple[int, int]


class CompletedDelivery(BaseModel):
    status: str
    timestamp: datetime


# For the input/output serialization of your handlers
@my_object.handler()
async def deliver(ctx: ObjectContext, delivery: Delivery) -> CompletedDelivery:

    # To serialize state
    await ctx.get("delivery", serde=PydanticJsonSerde(Delivery))
    ctx.set("delivery", delivery, serde=PydanticJsonSerde(Delivery))

    # To serialize awakeable payloads
    ctx.awakeable(serde=PydanticJsonSerde(Delivery))

    # To serialize the results of actions
    await ctx.run("some-task", some_task, serde=PydanticJsonSerde(Delivery))

    # etc.

    return CompletedDelivery(status="delivered", timestamp=datetime.now())

This is incorrect as the handler is unaware of how to deserialize the CompletedDelivery type correctly.

A relevant example for the issue is displayed further down on the page in this snippet:

# For the input/output serialization of your handlers
@my_object.handler(input_serde=MySerde(), output_serde=MySerde())
async def my_handler(ctx: ObjectContext, greeting: str) -> str:
    ...

where we learn how to pass deserializers to handlers.

So the correct pydantic example is

# For the input/output serialization of your handlers
@my_object.handler(output_serde=PydanticJsonSerde(CompletedDelivery))
async def deliver(ctx: ObjectContext, delivery: Delivery) -> CompletedDelivery:
    ...

[tillrohrmann]

Thanks for raising this issue @damianr13. Do we also need to add input_serde=PydanticJsonSerde(Delivery) for the input type @igalshilman?

[igalshilman]

@damianr13 the types are automatically deduced to be Pydantic. is it not the case for you?

[tillrohrmann]

Trying out the hello world Python example (where we are also using Pydantic input and output types), I was not able to reproduce the problem.

[damianr13]

Sorry for the late reply. I somehow missed the notification for this.

The problem is when the output is optional.

So in the python hello world example I triggered this by changing

async def greet(ctx: restate.Context, req: GreetingRequest) -> Greeting:

to

async def greet(ctx: restate.Context, req: GreetingRequest) -> Greeting | None:

So even when the function actually returns something, the service still crashes because of this type definition.