]
}
```

## Recap { #recap }

Declare headers with `Header`, using the same common pattern as `Query`, `Path` and `Cookie`.

Taking data from:

* The path as parameters.
* Headers.
* Cookies.
* etc.

And by doing so, **FastAPI** is validating that data, converting it and generating documentation for your API automatically.

But there are situations where you might need to access the `Request` object directly.

## Details about the `Request` object { #details-about-the-request-object }

{"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 <dfn title="converting the string that comes from an HTTP request into Python data">"parsing"</dfn>.

///

## Data validation { #data-validation }

  public void testBigToDouble() {
    for (BigInteger b : ALL_BIGINTEGER_CANDIDATES) {
      if (b.doubleValue() != DoubleUtils.bigToDouble(b)) {
        failFormat(
            "Converting %s to double: expected doubleValue %s but got bigToDouble %s",
            b, b.doubleValue(), DoubleUtils.bigToDouble(b));
      }
    }
  }

  public void testEnsureNonNegative() {

     */
    public ErrorToWarnRewritePolicy(final String[] loggerNames) {
        this.loggerNames = loggerNames;
    }

    /**
     * Rewrites log events by converting ERROR level to WARN level for matching loggers.
     *
     * @param event the log event to potentially rewrite
     * @return the original event or a new event with WARN level if conversion applied
     */
    @Override

import org.opensearch.search.SearchHit;

/**
 * Utility class for search engine operations and content formatting.
 * Provides helper methods for working with XContent builders, scrolling through search results,
 * and converting XContent objects to different output formats.
 */
public final class SearchEngineUtil {

    private static final Logger logger = LogManager.getLogger(SearchEngineUtil.class);

    /**

     */
    public RankFusionSearcher() {
        // Default constructor - name will be initialized lazily
    }

    /**
     * Returns the name of this searcher.
     * The name is derived from the class name by converting it to lowercase
     * and removing the "Searcher" suffix.
     *
     * @return the searcher name
     */
    public String getName() {
        if (name == null) {

of the main features needed by API systems is data "<dfn title="also called marshalling, conversion">serialization</dfn>" which is taking data from the code (Python) and converting it into something that can be sent through the network. For example, converting an object containing data from a database into a JSON object. Converting `datetime` objects into strings, etc.

Another big feature needed by APIs is data validation, making sure that the data is valid, given certain parameters. For...

 */

package jcifs.smb1.smb1;

/**
 * Interface defining DOS error codes and their mappings to NT status codes for SMB1 protocol.
 * Provides lookup tables for converting between DOS and NT error representations.
 */
public interface DosError {

    /**
     * Mapping table from DOS error codes to NT status codes.
     * Each entry contains a pair of [DOS error code, NT status code].

    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 <dfn title="converting the data to a format that can be transmitted">serializing</dfn> the data to JSON.

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