import os
from typing import Any, Dict, List

from pdm.backend.hooks import Context

TIANGOLO_BUILD_PACKAGE = os.getenv("TIANGOLO_BUILD_PACKAGE", "fastapi")


def pdm_build_initialize(context: Context) -> None:
    metadata = context.config.metadata
    # Get custom config for the current package, from the env var
    config: Dict[str, Any] = context.config.data["tool"]["tiangolo"][
        "_internal-slim-build"

 │                          │
 ╰──────────────────────────╯

<font color="#3465A4">INFO    </font> Using import string <font color="#8AE234"><b>main:app</b></font>

 │                          │
 ╰──────────────────────────╯

<font color="#3465A4">INFO    </font> Using import string <font color="#8AE234"><b>main:app</b></font>

from .param_functions import File as File
from .param_functions import Form as Form
from .param_functions import Header as Header
from .param_functions import Path as Path
from .param_functions import Query as Query
from .param_functions import Security as Security
from .requests import Request as Request
from .responses import Response as Response
from .routing import APIRouter as APIRouter
from .websockets import WebSocket as WebSocket

[tool.ruff.lint.isort]
known-third-party = ["fastapi", "pydantic", "starlette"]

[tool.ruff.lint.pyupgrade]
# Preserve types, even if a file imports `from __future__ import annotations`.

If you have *path operations* using `response_model` that need to be allowed to return `None`, make it explicit in `response_model` using `Union[Something, None]`:

```Python
from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: Optional[float] = None
    owner_ids: Optional[List[int]] = None

app = FastAPI()

 │                          │
 ╰──────────────────────────╯

<font color="#3465A4">INFO    </font> Using import string <font color="#8AE234"><b>main:app</b></font>

You write standard Python with types:

```Python
from datetime import date

from pydantic import BaseModel

# Declare a variable as a str
# and get editor support inside the function
def main(user_id: str):
    return user_id


# A Pydantic model
class User(BaseModel):
    id: int

In your **FastAPI** application, create a `websocket`:

```Python hl_lines="1  46-47"
{!../../../docs_src/websockets/tutorial001.py!}
```

!!! note "Technical Details"
    You could also use `from starlette.websockets import WebSocket`.

    **FastAPI** provides the same `WebSocket` directly just as a convenience for you, the developer. But it comes directly from Starlette.

## Await for messages and send messages

Now modify the file `main.py` to receive a body from a `PUT` request.

Declare the body using standard Python types, thanks to Pydantic.

```Python hl_lines="4  9-12  25-27"
from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


@app.get("/")