app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>Oder verwenden Sie <code>async def</code> ...</summary>

Wenn Ihr Code `async` / `await` verwendet, benutzen Sie `async def`:

```Python hl_lines="7  12"

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("We don't swallow the internal error here, we raise again 😎")
        raise


@app.get("/items/{item_id}")
def get_item(item_id: str, username: str = Depends(get_username)):
    if item_id == "portal-gun":

import os
import subprocess
import sys
from unittest.mock import patch

import fastapi.cli
import pytest


def test_fastapi_cli():
    result = subprocess.run(
        [
            sys.executable,
            "-m",
            "coverage",
            "run",
            "-m",
            "fastapi",
            "dev",
            "non_existent_file.py",
        ],
        capture_output=True,

).absolute()


@pytest.mark.parametrize(
    "copy_test_files",
    [(f"{data_path}/en_doc.md", f"{data_path}/translated_doc_mermaid_translated.md")],
    indirect=True,
)
def test_translated(runner: CliRunner, root_dir: Path, copy_test_files):
    result = runner.invoke(
        cli,
        ["fix-pages", "docs/lang/docs/doc.md"],
    )
    assert result.exit_code == 0, result.output

For example, you could declare that something could be a `str` or `None`:

```python
from typing import Union


def say_hi(name: Union[str, None]):
        print(f"Hi {name}!")
```

`typing` also has a shortcut to declare that something could be `None`, with `Optional`.

Here's a tip from my very **subjective** point of view:

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("We don't swallow the internal error here, we raise again 😎")
        raise


@app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):
    if item_id == "portal-gun":

	if !reflect.DeepEqual(v, v2) {
		t.Errorf("MSS: %v != %v", v, v2)
	}
}

func BenchmarkMarshalMsgMSS(b *testing.B) {
	v := MSS{"abc": "def", "ghi": "jkl"}
	b.ReportAllocs()

	for b.Loop() {
		v.MarshalMsg(nil)
	}
}

func BenchmarkAppendMsgMSS(b *testing.B) {
	v := MSS{"abc": "def", "ghi": "jkl"}
	bts := make([]byte, 0, v.Msgsize())
	bts, _ = v.MarshalMsg(bts[0:0])
	b.SetBytes(int64(len(bts)))
	b.ReportAllocs()

You can use `async def` or normal `def`.

And you can declare dependencies with `async def` inside of normal `def` *path operation functions*, or `def` dependencies inside of `async def` *path operation functions*, etc.

It doesn't matter. **FastAPI** will know what to do.

/// note

    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}


@app.get("/items/{item_id}", response_model=Item)
async def read_item(item_id: str):
    return items[item_id]


@app.put("/items/{item_id}", response_model=Item)
async def update_item(item_id: str, item: Item):
    update_item_encoded = jsonable_encoder(item)
    items[item_id] = update_item_encoded

    GradleVersion baseVersion
    Map<ApiChange, String> acceptedChanges

    static AcceptedApiChanges parse(List<String> jsonTexts) {
        def acceptedApiChanges = new AcceptedApiChanges()
        acceptedApiChanges.acceptedChanges = [:]
        for (String jsonText : jsonTexts) {
            def json = new Gson().fromJson(jsonText, new TypeToken<Map<String, List<AcceptedApiChange>>>() {}.type)