- login: Smlep
  count: 11
  avatarUrl: https://avatars.githubusercontent.com/u/16785985?v=4
  url: https://github.com/Smlep
- login: hard-coders
  count: 10
  avatarUrl: https://avatars.githubusercontent.com/u/9651103?u=95db33927bbff1ed1c07efddeb97ac2ff33068ed&v=4
  url: https://github.com/hard-coders
- login: alejsdev
  count: 10
  avatarUrl: https://avatars.githubusercontent.com/u/90076947?u=1ee3a9fbef27abc9448ef5951350f99c7d76f7af&v=4

```

### Declare a `list` with a type parameter

To declare types that have type parameters (internal types), like `list`, `dict`, `tuple`:

* If you are in a Python version lower than 3.9, import their equivalent version from the `typing` module
* Pass the internal type(s) as "type parameters" using square brackets: `[` and `]`

In Python 3.9 it would be:

```Python
my_list: list[str]
```

There you could buy me a coffee ☕️ to say thanks. 😄

And you can also become a Silver or Gold sponsor for FastAPI. 🏅🎉

## Sponsor the tools that power FastAPI

As you have seen in the documentation, FastAPI stands on the shoulders of giants, Starlette and Pydantic.

You can also sponsor:

Because this code is executed before the application **starts** taking requests, and right after it **finishes** handling requests, it covers the whole application **lifespan** (the word "lifespan" will be important in a second 😉).

So, `orion_cat.owner.name` could be the name (from the `name` column in the `owners` table) of this pet's owner.

It could have a value like `"Arquilian"`.

And the ORM will do all the work to get the information from the corresponding table *owners* when you try to access it from your pet object.

    username: str


class ModelC(ModelB):
    password: str


class ModelA(BaseModel):
    name: str
    description: Optional[str] = None
    model_b: ModelB

    @validator("name")
    def lower_username(cls, name: str, values):
        if not name.endswith("A"):
            raise ValueError("name must end in A")
        return name


async def get_model_c() -> ModelC:

## OAuth2

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

It includes ways to authenticate using a "third party".

That's what all the systems with "login with Facebook, Google, Twitter, GitHub" use underneath.

### OAuth 1

  - login: DMantis
    avatarUrl: https://avatars.githubusercontent.com/u/9536869?v=4
    url: https://github.com/DMantis
  - login: hard-coders
    avatarUrl: https://avatars.githubusercontent.com/u/9651103?u=95db33927bbff1ed1c07efddeb97ac2ff33068ed&v=4
    url: https://github.com/hard-coders
  - login: supdann
    avatarUrl: https://avatars.githubusercontent.com/u/9986994?u=9671810f4ae9504c063227fee34fd47567ff6954&v=4

To declare a **request** body, you use <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> models with all their power and benefits.

!!! info
    To send data, you should use one of: `POST` (the more common), `PUT`, `DELETE` or `PATCH`.

    Because of that, versions of FastAPI previous to 0.99.0 still used versions of OpenAPI lower than 3.1.0.

### Pydantic and FastAPI `examples`

When you add `examples` inside a Pydantic model, using `schema_extra` or `Field(examples=["something"])` that example is added to the **JSON Schema** for that Pydantic model.