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Example Code

# Removing the future imports allows the code to work as expected.
from __future__ import annotations

from fastapi import FastAPI 
from typing_extensions import Required, NotRequired, Literal, TypedDict

# IF you want to use OpenAI class as example, but not required.
# https://github.com/openai/openai-python/blob/da48e4cac78d1d4ac749e2aa5cfd619fde1e6c68/src/openai/types/chat/chat_completion_system_message_param.py
# from openai.types.chat.chat_completion_system_message_param import ChatCompletionSystemMessageParam

app = FastAPI()

class RequiredTypedDictExample(TypedDict, total=False):
    name: Required[str]= "This is required"
    age: int

class NonRequiredTypedDictExample(TypedDict, total=False):
    name: NotRequired[str]
    age: int

@app.post("/RequiredTypeDict")
async def something_to_post(request: RequiredTypedDictExample):
    return {"message": "Hello World"}

@app.post("/NonRequiredTypedDictExample")
async def something_to_post_2(request: NonRequiredTypedDictExample):
    return {"message": "Hello World"}

# @app.post("/OpenAITestCase")
# async def something_to_post_3(request: ChatCompletionSystemMessageParam):
#     return {"message": "Hello World"}

Description

Running a simple example with a POST endpoint that expects a request parameter defined by a TypedDict class results in an error within Pydantic about

TypeError: 'pydantic_core._pydantic_core.PydanticUndefinedType' object is not subscriptable

Trying to dig into the issue more lead me to see that the Required attribute / import is being redefined as PydanticUndefined in the file here

When importing types defined by other modules / classes it isn't always possible to change.

If you run the above, but remove the from __future__ import annotations, the code runs and performs as expected.

Not sure why the futures import causes issues here, but with this I am unable to use classes / datatypes defined in other modules that make use of this python feature.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.112.0

Pydantic Version

2.8.2

Python Version

Python 3.12.2

Additional Context

No response