Fix bug related to Azure OpenAI model streaming response

[gbe3hunna]

Solves: #797

This PR fixes an issue happening with Azure OpenAI streaming Response causing the raise of an AttributeError

As stated on the issue, the error occurs in pydantic-ai's OpenAI model implementation where it assumes every delta in the streaming response contains a content field. However, with Azure OpenAI's API, some deltas (like role initialization) may not include content, resulting in choice.delta.content being None.

[sydney-runkle]

Wonderful, thanks :)

[sydney-runkle]

Could you please take a look at the linting issue? Thanks!

[gbe3hunna]

Seems the linting issue is happening because the Choice BaseModel defines the field delta as ChoiceDelta, and not as an Optional[ChoiceDelta] or ChoiceDelta | None, which is the case exposed at #797 (comment)

class Choice(BaseModel):
    delta: ChoiceDelta
    """A chat completion delta generated by streamed model responses."""
    ...

I couldn't reproduce the problem for now

CI pyright output: /home/runner/work/pydantic-ai/pydantic-ai/pydantic_ai_slim/pydantic_ai/models/openai.py:356:16 - error: Condition will always evaluate to True since the types "ChoiceDelta" and "None" have no overlap (reportUnnecessaryComparison)

[Kludex]

I'm trying to get some Azure AI Foundry keys so I can add a test for this.

[Kludex]

@gbe3hunna can you give me the snippet that reproduces this issue? I can't reproduce it.

[gbe3hunna]

@gbe3hunna can you give me the snippet that reproduces this issue? I can't reproduce it.

Nope. I just took the issue but already mentioned I cannot reproduce it

[Kludex]

If we can't reproduce, then I think we can close it. Thanks for the help!

[martgra]

@Kludex Ref comment in #797 - how can I help to reproduce. As mentioned in issue - this occurs only with async content filter enabled. https://learn.microsoft.com/en-us/azure/ai-services/openai/concepts/content-filter?tabs=warning%2Cuser-prompt%2Cpython-new#asynchronous-filter

@gbe3hunna