/// tip

The next sections are **not necessarily "advanced"**.

And it's possible that for your use case, the solution is in one of them.

///

## Read the Tutorial first { #read-the-tutorial-first }

You could still use most of the features in **FastAPI** with the knowledge from the main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank}.

      CertificatePinner
        .Builder()
        .add("first.com", certA1Sha256Pin, certB1Sha256Pin)
        .add("second.com", certC1Sha256Pin)
        .build()

    val expectedPins =
      listOf(
        Pin("first.com", certA1Sha256Pin),
        Pin("first.com", certB1Sha256Pin),
      )
    assertThat(certificatePinner.findMatchingPins("first.com")).isEqualTo(expectedPins)
  }

```Python
if "johndoe" == "stanleyjobson" and "love123" == "swordfish":
    ...
```

  @Override
  public @Nullable Comparator<? super E> comparator() {
    return delegate().comparator();
  }

  @Override
  @ParametricNullness
  public E first() {
    return delegate().first();
  }

  @Override
  public SortedSet<E> headSet(@ParametricNullness E toElement) {
    return delegate().headSet(toElement);
  }

  @Override
  @ParametricNullness
  public E last() {

    @Override
    public int compare(@Nullable String first, @Nullable String second) {
      if (first == second) {
        return 0;
      } else if (first == null) {
        return -1;
      } else if (second == null) {
        return 1;
      } else if (first.length() != second.length()) {
        return first.length() - second.length();
      } else {
        return first.compareTo(second);
      }
    }
  }

   *
   * @param first the first element
   * @param rest an array of additional elements, possibly empty
   * @return an unmodifiable list containing the specified elements
   */
  public static <E extends @Nullable Object> List<E> asList(@ParametricNullness E first, E[] rest) {
    return new OnePlusArrayList<>(first, rest);
  }

  /**

  }

  @SuppressWarnings("unused") // compilation test
  public void testSampleCodeError2() {
    FluentIterable<? extends Number> numbers = getSomeNumbers();
    Optional<? extends Number> first = numbers.first();
    // Number value = first.or(0.5); // error
  }

  @SuppressWarnings("unused") // compilation test
  public void testSampleCodeFine1() {
    Optional<Number> optionalInt = Optional.of((Number) 1);

//
//	// Find the first user with name jinzhu
//	db.Where("name = ?", "jinzhu").First(&user)
//	// Find the first user with name jinzhu and age 20
//	db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
//	// Find the first user with name jinzhu and age not equal to 20
//	db.Where("name = ?", "jinzhu").Where("age <> ?", "20").First(&user)
//
// [docs]: https://gorm.io/docs/query.html#Conditions

    return user


@app.get("/users/me")
def read_current_user(current_user: Optional[User] = Depends(get_current_user)):
    if current_user is None:
        return {"msg": "Create an account first"}
    return current_user


client = TestClient(app)


def test_security_api_key():
    response = client.get("/users/me", headers={"key": "secret"})
    assert response.status_code == 200, response.text

You can create dependencies that have **sub-dependencies**.

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.