from dataclasses import dataclass, field

from fastapi import FastAPI


@dataclass
class Item:
    name: str
    price: float
    tags: list[str] = field(default_factory=list)
    description: str | None = None
    tax: float | None = None


app = FastAPI()


@app.get("/items/next", response_model=Item)
async def read_next_item():
    return {
        "name": "Island In The Moon",
        "price": 12.99,

    assert response.json() == {
        "sub_items": [{"name": "subitem", "sub_items": []}],
        "name": "item",
    }

    response = client.get("/items/recursive-submodel")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "name": "item",
        "sub_items1": [
            {
                "name": "subitem",
                "sub_items2": [
                    {

    response = client.put("/items/5", json={"item": {"name": "Foo", "price": 3.0}})
    assert response.status_code == 200
    assert response.json() == {
        "item_id": 5,
        "item": {"name": "Foo", "price": 3.0, "description": None, "tax": None},
    }


def test_items_6(client: TestClient):
    response = client.put(
        "/items/6",
        json={
            "item": {
                "name": "Bar",

///

## Writing templates { #writing-templates }

Then you can write a template at `templates/item.html` with, for example:

```jinja hl_lines="7"
{!../../docs_src/templates/templates/item.html!}
```

### Template Context Values { #template-context-values }

In the HTML that contains:

{% raw %}

```jinja
Item ID: {{ id }}
```

{% endraw %}

                        + LS
                        + LS + "<configuration>"
                        + LS + "  ..."
                        + LS + "  <toAddresses>"
                        + LS + "    <item>VALUE</item>"
                        + LS + "  </toAddresses>"
                        + LS + "</configuration>."
                        + LS,
                exception.buildDiagnosticMessage());
    }

    @Test

    The first one to _not_ be a `DefaultPlaceholder` will be returned.

    Otherwise, the first item (a `DefaultPlaceholder`) will be returned.
    """
    items = (first_item,) + extra_items
    for item in items:
        if not isinstance(item, DefaultPlaceholder):
            return item

        raise HTTPException(status_code=400, detail="X-Key header invalid")
    return x_key


@app.get("/items/", dependencies=[Depends(verify_token), Depends(verify_key)])
async def read_items():

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: float = 10.5
    tags: list[str] = []


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/{item_id}")
async def read_user_item(
    item_id: str, needy: str, skip: int = 0, limit: int | None = None
):
    item = {"item_id": item_id, "needy": needy, "skip": skip, "limit": limit}

If you want to receive partial updates, it's very useful to use the parameter `exclude_unset` in Pydantic's model's `.model_dump()`.

Like `item.model_dump(exclude_unset=True)`.

That would generate a `dict` with only the data that was set when creating the `item` model, excluding default values.

Then you can use this to generate a `dict` with only the data that was set (sent in the request), omitting default values: