But Python has a specific way to declare lists with internal types, or "type parameters":

### Import typing's `List`

In Python 3.9 and above you can use the standard `list` to declare these type annotations as we'll see below. 💡

But in Python versions before 3.9 (3.6 and above), you first need to import `List` from standard Python's `typing` module:

```Python hl_lines="1"
{!> ../../../docs_src/body_nested_models/tutorial002.py!}
```

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`.

### Short

<div class="termy">

```console
$ pip install "uvicorn[standard]"

---> 100%
```

</div>

## Exemplo

### Crie

* Crie um arquivo `main.py` com:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


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


@app.get("/items/{item_id}")

### Import `Query` and `Annotated`

To achieve that, first import:

* `Query` from `fastapi`
* `Annotated` from `typing` (or from `typing_extensions` in Python below 3.9)

=== "Python 3.10+"

    In Python 3.9 or above, `Annotated` is part of the standard library, so you can import it from `typing`.

    ```Python hl_lines="1  3"
    {!> ../../../docs_src/query_params_str_validations/tutorial002_an_py310.py!}
    ```

```

Here the query parameter `needy` is a required query parameter of type `str`.

If you open in your browser a URL like:

```
http://127.0.0.1:8000/items/foo-item
```

...without adding the required parameter `needy`, you will see an error like:

```JSON
{
  "detail": [
    {
      "type": "missing",
      "loc": [
        "query",
        "needy"
      ],

```console
$ pip install "uvicorn[standard]"

---> 100%
```

</div>

## Nümunə

### Kodu yaradaq

* `main.py` adlı fayl yaradaq və ona aşağıdakı kodu yerləşdirək:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


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


@app.get("/items/{item_id}")

```console
$ pip install "uvicorn[standard]"

---> 100%
```

</div>

## Ví dụ

### Khởi tạo

* Tạo một tệp tin `main.py` như sau:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


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


@app.get("/items/{item_id}")

```console
$ pip install "uvicorn[standard]"

---> 100%
```

</div>

## Àpẹẹrẹ

### Ṣẹ̀dá rẹ̀

* Ṣẹ̀dá fáìlì `main.py (èyí tíí ṣe, akọkọ.py)` pẹ̀lú:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


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


@app.get("/items/{item_id}")

## The normal **FastAPI** app

Let's first see how the normal API app would look like before adding the callback.

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

* Valida **estruturas complexas**:
    * Use modelos hierárquicos do Pydantic, `List` e `Dict` do `typing` do Python, etc.
    * Validadores permitem que esquemas de dados complexos sejam limpos e facilmente definidos, conferidos e documentados como JSON Schema.