For example, you cannot put a Pydantic model in a `JSONResponse` without first converting it to a `dict` with all the data types (like `datetime`, `UUID`, etc) converted to JSON-compatible types.

For those cases, you can use the `jsonable_encoder` to convert your data before passing it to a response:

It would also mean that if you get data from the `Request` object directly (for example, read the body) it won't be validated, converted or documented (with OpenAPI, for the automatic API user interface) by FastAPI.

Although any other parameter declared normally (for example, the body with a Pydantic model) would still be validated, converted, annotated, etc.

But there are specific cases where it's useful to get the `Request` object.

* `frozenset`:
    * In requests and responses, treated the same as a `set`:
        * In requests, a list will be read, eliminating duplicates and converting it to a `set`.
        * In responses, the `set` will be converted to a `list`.
        * The generated schema will specify that the `set` values are unique (using JSON Schema's `uniqueItems`).
* `bytes`:
    * Standard Python `bytes`.

    In this case, it's a list of `Item` dataclasses.

6. Here we are returning a dictionary that contains `items` which is a list of dataclasses.

    FastAPI is still capable of <abbr title="converting the data to a format that can be transmitted">serializing</abbr> the data to JSON.

7. Here the `response_model` is using a type annotation of a list of `Author` dataclasses.

    * JSON.
    * Pad parameters.
    * Query parameters.
    * Cookies.
    * Headers.
    * Formulieren.
    * Bestanden.
* <abbr title="ook bekend als: serialisatie, parsing, marshalling">Conversie</abbr> van uitvoergegevens: converstie van Python-data en -types naar netwerkgegevens (zoals JSON):

{"item_id":3}
```

/// check | Revisa

Nota que el valor que tu función recibió (y devolvió) es `3`, como un `int` de Python, no un string `"3"`.

Entonces, con esa declaración de tipo, **FastAPI** te ofrece <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr> automático de requests.

///

## Validación de datos

{"item_id":3}
```

/// 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 { #data-validation }

   *     specified is substituted for the first occurrence of {@code "%s"} in the template, and so
   *     forth. A {@code null} argument is converted to the four-character string {@code "null"};
   *     non-null values are converted to strings using {@link Object#toString()}.
   * @since 25.1
   */
  // TODO(diamondm) consider using Arrays.toString() for array parameters
  public static String lenientFormat(

        return bufferIndex - start;
    }

    @Override
    public String toString() {
        return ("NetShareEnumResponse[" + super.toString() + ",status=" + getStatus() + ",converter=" + this.converter + ",entriesReturned="
                + getNumEntries() + ",totalAvailableEntries=" + this.totalAvailableEntries + "]");
    }

        return bufferIndex - start;
    }

    @Override
    public String toString() {
        return ("NetServerEnum2Response[" + super.toString() + ",status=" + status + ",converter=" + converter + ",entriesReturned="
                + numEntries + ",totalAvailableEntries=" + totalAvailableEntries + ",lastName=" + lastName + "]");
    }