PYTHON PIZZA ISTANBUL · 14 NOV 2026

A Slice ofFastAPI

In 10 minutes, still hot.

Erhan BÜTE erhan.dev

Hi! I’m Slice 👋

FastAPI’s recipe

A modern, fast, type-hint-driven Python web framework.

OpenAPI The toppings
automatic documentation
Type hints The cheese
binds it all together
Pydantic The sauce
validation & serialization
Starlette The dough
ASGI, routing, async

= FastAPI

That’s the whole recipe.

Margherita: the classic

Three lines, one working API.

examples/01_hello.py main.py

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root() -> dict[str, str]:
    return {"message": "Merhaba Python Pizza! 🍕"}

3 lines
0 config
reloads by itself

terminal

$ uv run fastapi dev examples/01_hello.py
 ⚡️ Starting FastAPI in development mode
 🌐 Server started at http://127.0.0.1:8000
    Documentation at http://127.0.0.1:8000/docs

127.0.0.1:8000

{
  "message": "Merhaba Python Pizza! 🍕"
}

Seriously, three lines.

Four Cheese

Where does the data come from? One function, four sources.

examples/02_params.py

@app.post("/pizzas/{pizza_id}/orders")
async def order_pizza(
    pizza_id: int,  # path
    order: Order,  # body
    extra_cheese: bool = False,  # query
    x_table_no: Annotated[int | None, Header()] = None,  # header
) -> dict[str, object]:
    return {
        "pizza_id": pizza_id,
        "extra_cheese": extra_cheese,
        "table": x_table_no,
        "order": order,
    }

Path in the URL

/pizzas/3/orders → pizza_id = 3

Query after the ?

?extra_cheese=true → extra_cheese = True

Header in the headers

X-Table-No: 7 → x_table_no = 7

Body in the JSON

{"customer": "Ayşe", "quantity": 2} → order = Order(…)

422 pizza_id: int → a request to /pizzas/abc is rejected before your function runs.

All from type hints.

The Pineapple Test

We wrote no validation code. Pineapple was still rejected.

examples/03_models.py

class Topping(StrEnum):
    mozzarella = "mozzarella"
    pepperoni = "pepperoni"
    mushroom = "mushroom"
    basil = "basil"  # pineapple? not on this menu!


class PizzaCreate(BaseModel):
    name: str = Field(min_length=2, max_length=40)
    price: int = Field(gt=0)
    toppings: list[Topping] = Field(min_length=1)

curl · Swagger UI · Postman…

POST/pizzasValid request

{"name": "Margherita", "price": 190, "toppings": ["mozzarella", "basil"]}

201 Created

{
  "name": "Margherita",
  "price": 190,
  "toppings": ["mozzarella", "basil"]
}

POST/pizzasPineapple request

{"name": "Hawaii", "price": 200, "toppings": ["mozzarella", "ananas"]}

422 Unprocessable Content

{
  "detail": [{
    "loc": ["body", "toppings", 1],
    "msg": "Input should be 'mozzarella', 'pepperoni', 'mushroom' or 'basil'",
    "input": "ananas"
  }]
}

201Pizza is cooking
404No such pizza
422Pineapple detected!
418You wanted tea, I’m a teapot ☕

PINEAPPLE?!

The menu writes itself

Without writing a single line of docs.

/docs Swagger UI
/redoc ReDoc
/openapi.json machine-readable schema

The automatically generated Swagger UI page of the Pizza API

The 422 response to a pineapple request in Swagger UI

I didn’t write it, I swear.

Depends: your sous-chef

The chef just makes pizza. The kitchen brings the ingredients.

examples/04_depends.py

def pagination(limit: int = 10, offset: int = 0) -> dict[str, int]:
    return {"limit": limit, "offset": offset}

Pagination = Annotated[dict[str, int], Depends(pagination)]

@app.get("/menu")
async def menu(page: Pagination): ...

def require_chef(x_api_key: Annotated[str | None, Header()] = None):
    if x_api_key != "chef-secret":
        raise HTTPException(401, "Only the chef can do that 👨‍🍳")

@app.delete("/menu/{name}", dependencies=[Depends(require_chef)])
async def remove(name: str): ...

yield = cleanup when done. FastAPI does the dishes 🧽

📄 pagination() limit & offset

🔑 require_chef() authorization

🗄️ get_db() database session

route function @app.get · @app.delete

app/core/db.py

async def get_db() -> AsyncIterator[AsyncSession]:
    async with SessionLocal() as session:
        yield session

Ingredients ready, chef!

async def: one waiter, many tables

Three orders at once. How many waiters do you need?

examples/05_async.py

@app.get("/bake/async")
async def bake_async():
    await asyncio.sleep(BAKE_SECONDS)  # waiter serves other tables ✅

@app.get("/bake/blocking")
async def bake_blocking():
    time.sleep(BAKE_SECONDS)  # waiter freezes at the oven ❌

@app.get("/bake/threadpool")
def bake_threadpool():
    time.sleep(BAKE_SECONDS)  # `def` runs in a thread pool ✅

The waiter stands at the oven6.05 s

Table 1

Table 2

Table 3

The waiter serves other tables while the oven works2.05 s

Table 1

Table 2

Table 3

⏱ Measured for real: 3 concurrent requests

awaitserve other tables while the oven works
defFastAPI runs you in a thread pool
async def + time.sleep()the waiter freezes at the oven

I’m the only waiter 😅

A growing restaurant: kitchen layout

Requests flow from top to bottom.

fastapi-pizza/

├── app/

│ ├── main.py 🚀 create_app() lifespan

│ ├── api/ 🛎️ Waiter routes + dependencies

│ ├── schemas/ 🧾 Menu & receipt Pydantic models

│ ├── services/ 👨‍🍳 Chef business rules

│ ├── crud/ 🥫 Pantry database queries

│ ├── models/ 📖 Recipe book tables

│ └── core/ 🔧 Equipment settings, DB, errors

├── examples/ the code on these slides

└── tests/ taste first

🌐Request

🛎️route · api/

👨‍🍳service · services/

🥫crud · crud/

🗄️DB · models/

A place for everything.

Taste it first

TestClient: no server needed, done in seconds.

tests/test_pizzas.py pytest

def test_pineapple_is_rejected(client: TestClient, chef: dict[str, str]) -> None:
    body = {"name": "Hawaii", "price": 200, "toppings": ["mozzarella", "ananas"]}
    response = client.post(URL, json=body, headers=chef)
    assert response.status_code == 422
    error = response.json()["detail"][0]
    assert error["loc"] == ["body", "toppings", 1]
    assert error["input"] == "ananas"
    assert client.get(URL).json() == []  # nothing was created

terminal

$ uv run pytest -v
tests/test_pizzas.py::test_pizza_id_must_be_an_int PASSED        [ 65%]
tests/test_pizzas.py::test_pineapple_is_rejected PASSED          [ 70%]
============================== 44 passed in 2.07s ==============================

Mmm… that 422 is spot on.

Serve it hot

From local to live in three commands.

$ fastapi dev development

auto-reload

$ fastapi run production

one command, ready server

$ fastapi deploy FastAPI Cloud

live in one command

Docker or plain uvicorn on your own server work too.

Piping hot!

The check, please!

PIZZA API · RECEIPT

14 November 2026 · StartGate, Maslak, Istanbul

Type hintsvalidation + docs
4 × cheesepath · query · header · body
Pydanticpineapple rejection
/docsthe menu writes itself
Dependsthe kitchen brings ingredients
asyncone waiter, many tables
TestClienttaste first

TOTAL10 min

Tip: ⭐ the repo

AFİYET OLSUN

It’s on me.

Afiyet olsun!

Questions? (No pineapple.)

Thank you! 👋

Slides python-pizza.erhan.dev/en

Example code github.com/erhan/fastapi-pizza

A Slice ofFastAPI

Peek at the slides

Today’s menu

Starters

Main course

Dessert

A Slice ofFastAPI

Menu

Starters

Dessert

Main course

FastAPI’s recipe

Margherita: the classic

Four Cheese

The Pineapple Test

The menu writes itself

Depends: your sous-chef

async def: one waiter, many tables

A growing restaurant: kitchen layout

Taste it first

Serve it hot

The check, please!

PIZZA API · RECEIPT

Afiyet olsun!

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