They can be as **deep** as you need them to be.

**FastAPI** will take care of solving them.

## First dependency "dependable" { #first-dependency-dependable }

You could create a first dependency ("dependable") like:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

It declares an optional query parameter `q` as a `str`, and then it just returns it.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

You can think of it as a *path operation function* without the "decorator" (without the `@app.get("/some-path")`).

    val slot = 0

    val config = "--name=OpenSC\nlibrary=/Library/OpenSC/lib/opensc-pkcs11.so\nslot=$slot\n"

    // May fail with ProviderException with root cause like
    // sun.security.pkcs11.wrapper.PKCS11Exception: CKR_SLOT_ID_INVALID
    val pkcs11 = Security.getProvider("SunPKCS11").configure(config)
    Security.addProvider(pkcs11)

    val callbackHandler = ConsoleCallbackHandler

    try {
      long remainingNanos = unit.toNanos(timeout);
      long end = System.nanoTime() + remainingNanos;

      while (true) {
        try {
          // TimeUnit.timedJoin() treats negative timeouts just like zero.
          NANOSECONDS.timedJoin(thread, remainingNanos);
          return;
        } catch (InterruptedException e) {
          interrupted = true;
          remainingNanos = end - System.nanoTime();
        }

     *
     * @return the protocol of the proxy server
     */
    public String getProtocol() {
        return protocol;
    }

    /**
     * @param protocol the protocol of the proxy server like <i>SOCKSv4</i>
     */
    public void setProtocol(String protocol) {
        this.protocol = protocol;
    }

    public String getNonProxyHosts() {
        return nonProxyHosts;
    }

///

## Dependencies errors and return values { #dependencies-errors-and-return-values }

You can use the same dependency *functions* you use normally.

### Dependency requirements { #dependency-requirements }

They can declare request requirements (like headers) or other sub-dependencies:

* <a href="https://www.uvicorn.org/" class="external-link" target="_blank">Uvicorn</a> : un serveur ASGI haute performance.
* <a href="https://hypercorn.readthedocs.io/" class="external-link" target="_blank">Hypercorn</a> : un serveur
  ASGI compatible avec HTTP/2 et Trio entre autres fonctionnalités.
* <a href="https://github.com/django/daphne" class="external-link" target="_blank">Daphne</a> : le serveur ASGI
  conçu pour Django Channels.

/**
 * Implementation helper for {@link EqualsTester} and {@link EquivalenceTester} that tests for
 * equivalence classes.
 *
 * @author Gregory Kick
 */
@GwtCompatible
@NullMarked
final class RelationshipTester<T> {
  interface ItemReporter {
    String reportItem(Item<?> item);
  }

  /**
   * A word about using {@link Equivalence}, which automatically checks for {@code null} and

{* ../../docs_src/query_params/tutorial005.py hl[6:7] *}

Hier ist `needy` ein erforderlicher Query-Parameter vom Typ `str`.

Wenn Sie in Ihrem Browser eine URL wie:

```
http://127.0.0.1:8000/items/foo-item
```

... öffnen, ohne den benötigten Parameter `needy`, dann erhalten Sie einen Fehler wie den folgenden:

```JSON
{
  "detail": [
    {

///

The `status_code` parameter receives a number with the HTTP status code.

/// info

`status_code` can alternatively also receive an `IntEnum`, such as Python's <a href="https://docs.python.org/3/library/http.html#http.HTTPStatus" class="external-link" target="_blank">`http.HTTPStatus`</a>.

///

It will: