```Python hl_lines="2  7 8 9 10  23 24 25"
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool = None


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


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

```Python hl_lines="4  9 10 11 12  25 26 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("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):

*  `prices` değişkeni `dict` tipindedir:
    *  `dict` değişkeninin `key` değeri  `str` tipindedir (herbir item'ın "name" değeri).
    *  `dict` değişkeninin `value` değeri `float` tipindedir (lherbir item'ın "price" değeri).

#### `Optional`

`Optional` bir değişkenin `str`gibi bir tipi olabileceğini ama isteğe bağlı olarak tipinin `None` olabileceğini belirtir:

```Python hl_lines="1  4"

Por ejemplo, cuando escribes `python` en la terminal, el sistema operativo busca un programa llamado `python` en el **primer directorio** de esa lista.

Si lo encuentra, entonces lo **utilizará**. De lo contrario, continúa buscando en los **otros directorios**.

	{"X1", "X1"},
	{"X2", "X2"},
	{"X3", "X3"},
	{"X4", "X4"},
	{"X5", "X5"},
	{"X6", "X6"},
	{"X7", "X7"},
	{"asmcgocall<>(SB)", "asmcgocall<>(SB)"},
	{"ax+4(FP)", "ax+4(FP)"},
	{"ptime-12(SP)", "ptime-12(SP)"},
	{"runtime·_NtWaitForSingleObject(SB)", "runtime._NtWaitForSingleObject(SB)"},
	{"s(FP)", "s(FP)"},
	{"sec+4(FP)", "sec+4(FP)"},
	{"shifts<>(SB)(CX*8)", "shifts<>(SB)(CX*8)"},
	{"x+4(FP)", "x+4(FP)"},

![Editor Unterstützung](https://fastapi.tiangolo.com/img/pycharm-completion.png)

Sie bekommen sogar Autovervollständigung an Stellen, an denen Sie dies vorher nicht für möglich gehalten hätten. Zum Beispiel der `price` Schlüssel in einem JSON Datensatz (dieser könnte auch verschachtelt sein), der aus einem Request kommt.

![editor support](https://fastapi.tiangolo.com/img/pycharm-completion.png)

You will get completion in code you might even consider impossible before. As for example, the `price` key inside a JSON body (that could have been nested) that comes from a request.

No more typing the wrong key names, coming back and forth between docs, or scrolling up and down to find if you finally used `username` or `user_name`.

![editor support](https://fastapi.tiangolo.com/img/pycharm-completion.png)


Daha önceden düşünüp en imkansız diyebileceğin durumlarda bile otomatik tamamlama alacaksın, örnek olarak `price` JSON body içerisinde (nested bir JSON body de olabilirdi.) direkt olarak istekten geliyor, bu durumda bile oto-tammalama sağlıyor.

 *
 * <p>This class should not be assumed to be universally superior to {@code
 * java.util.LinkedHashSet}. Generally speaking, this class reduces object allocation and memory
 * consumption at the price of moderately increased constant factors of CPU. Only use this class
 * when there is a specific reason to prioritize memory over CPU.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible // not worth using in GWT for now

 *
 * <p>This class should not be assumed to be universally superior to {@code
 * java.util.LinkedHashSet}. Generally speaking, this class reduces object allocation and memory
 * consumption at the price of moderately increased constant factors of CPU. Only use this class
 * when there is a specific reason to prioritize memory over CPU.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible // not worth using in GWT for now