# Using Dataclasses { #using-dataclasses }

FastAPI is built on top of **Pydantic**, and I have been showing you how to use Pydantic models to declare requests and responses.

But FastAPI also supports using <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> the same way:

{* ../../docs_src/dataclasses/tutorial001.py hl[1,7:12,19:20] *}

///

This is of course not the frontend for the final users, but it's a great automatic tool to document interactively all your API.

It can be used by the frontend team (that can also be yourself).

It can be used by third party applications and systems.

And it can also be used by yourself, to debug, check and test the same application.

## The `password` flow { #the-password-flow }

Now let's go back a bit and understand what is all that.

for the Android flavor.

[Snapshot API Javadoc][guava-snapshot-api-docs] as well as
[Snapshot API Diffs][guava-snapshot-api-diffs] are also available.

Another easy way to get to the Javadoc is to open
[guava.dev/api](https://guava.dev/api). You can also jump right to a specific
class by appending the class name to guava.dev. For example,
[guava.dev/ImmutableList](https://guava.dev/ImmutableList)!

## Learn about Guava

Pass `*`, as the first parameter of the function.

Python won't do anything with that `*`, but it will know that all the following parameters should be called as keyword arguments (key-value pairs), also known as <abbr title="From: K-ey W-ord Arg-uments"><code>kwargs</code></abbr>. Even if they don't have a default value.

{* ../../docs_src/path_params_numeric_validations/tutorial003.py hl[7] *}

        override fun contentLength(): Long = 10

        override fun source(): BufferedSource = Buffer().writeUtf8("hello")
      }
    assertFailsWith<IOException> {
      body.bytes()
    }.also { expected ->
      assertThat(expected.message).isEqualTo(
        "Content-Length (10) and stream length (5) disagree",
      )
    }
  }

  @Test
  fun bytesThrowsMoreThanIntMaxValue() {

Let's focus on the parameters declared:

* Even though this function is a dependency ("dependable") itself, it also declares another dependency (it "depends" on something else).
    * It depends on the `query_extractor`, and assigns the value returned by it to the parameter `q`.
* It also declares an optional `last_query` cookie, as a `str`.

It has the same fields as `HeroBase`, and it also has `secret_name`.

Now, when the clients **create a new hero**, they will send the `secret_name`, it will be stored in the database, but those secret names won't be returned in the API to the clients.

/// tip

This is how you would handle **passwords**. Receive them, but don't return them in the API.

<img src="/img/python-types/image04.png">

Now you know that you have to fix it, convert `age` to a string with `str(age)`:

{* ../../docs_src/python_types/tutorial004.py hl[2] *}

## Declaring types { #declaring-types }

You just saw the main place to declare type hints. As function parameters.

This is also the main place you would use them with **FastAPI**.

# Response Status Code { #response-status-code }

The same way you can specify a response model, you can also declare the HTTP status code used for the response with the parameter `status_code` in any of the *path operations*:

* `@app.get()`
* `@app.post()`
* `@app.put()`
* `@app.delete()`
* etc.

{* ../../docs_src/response_status_code/tutorial001.py hl[6] *}

/// note

The spec also states that the `username` and `password` must be sent as form data (so, no JSON here).

### `scope` { #scope }

The spec also says that the client can send another form field "`scope`".