A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.
* Then it passes the **request** to be processed by the rest of the application (by some *path operation*).

    You could also use `from starlette.staticfiles import StaticFiles`.

    **FastAPI** provides the same `starlette.staticfiles` as `fastapi.staticfiles` just as a convenience for you, the developer. But it actually comes directly from Starlette.

### What is "Mounting"

"Mounting" means adding a complete "independent" application in a specific path, that then takes care of handling all the sub-paths.

!!! check
    Notice that the value your function received (and returned) is `3`, as a Python `int`, not a string `"3"`.

    So, with that type declaration, **FastAPI** gives you automatic request <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>.

## Data validation

The main thing you need to run a **FastAPI** application (or any other ASGI application) in a remote server machine is an ASGI server program like **Uvicorn**, this is the one that comes by default in the `fastapi` command.

There are several alternatives, including:

* <a href="https://www.uvicorn.org/" class="external-link" target="_blank">Uvicorn</a>: a high performance ASGI server.

!!! note "Technical Details"
    You could also use `from starlette.testclient import TestClient`.

    **FastAPI** provides the same `starlette.testclient` as `fastapi.testclient` just as a convenience for you, the developer. But it comes directly from Starlette.

!!! tip

We are already halfway there.

We just need to add a *path operation* for the user/client to actually send the `username` and `password`.

    {!> ../../../docs_src/path_params_numeric_validations/tutorial005.py!}
    ```

## Number validations: floats, greater than and less than

Number validations also work for `float` values.

They have proven to be **FastAPI Experts** by helping many others. ✨

!!! tip
    You could become an official FastAPI Expert too!

    Just [help others with questions in GitHub](help-fastapi.md#help-others-with-questions-in-github){.internal-link target=_blank}. 🤓

You can see the **FastAPI Experts** for:

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str


items = [
    {"name": "Foo", "description": "There comes my hero"},
    {"name": "Red", "description": "It's my aeroplane"},
]


@app.get("/items/", response_model=List[Item])
async def read_items():

@needs_py39
def test_get_items(client: TestClient):
    response = client.get("/items/")
    assert response.status_code == 200, response.text
    assert response.json() == [
        {"name": "Foo", "description": "There comes my hero"},
        {"name": "Red", "description": "It's my aeroplane"},
    ]


@needs_py39
def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")