* One has to write NullAway-conformant code even when hacking.
* Some patterns used to satisfy NullAway can be slightly more verbose.

{* ../../docs_src/bigger_applications/app_an_py310/routers/items.py hl[3] title["app/routers/items.py"] *}

#### How relative imports work { #how-relative-imports-work }

/// tip

If you know perfectly how imports work, continue to the next section below.

///

A single dot `.`, like in:

```Python
from .dependencies import get_token_header
```

would mean:

/**
 * Strategy interface for different types of upgrade operations.
 * Each strategy handles a specific aspect of the Maven upgrade process.
 *
 * <p>Strategies work with domtrip Documents for perfect formatting preservation.
 * Individual strategies can create domtrip Editors from Documents as needed:
 * <pre>
 * Editor editor = new Editor(document);
 * // ... perform domtrip operations ...

/**
 * Abstract base class for upgrade strategies that provides common functionality
 * and reduces code duplication across strategy implementations.
 *
 * <p>Strategies work with domtrip Documents for perfect formatting preservation.
 * Subclasses can create domtrip Editors from Documents as needed:
 * <pre>
 * Editor editor = new Editor(document);
 * // ... perform domtrip operations ...
 * // Document is automatically updated

     * Apply goals return true, Check goals return false.
     */
    protected abstract boolean shouldSaveModifications();

    /**
     * Saves the modified documents to disk using domtrip's perfect formatting preservation.
     */
    protected void saveModifications(UpgradeContext context, Map<Path, Document> pomMap) {
        context.info("");
        context.info("Saving modified POMs...");

        assertTrue(StrictMath.pow(2.0, log2 + 1) > d);
      }
    }
  }

  @GwtIncompatible // DoubleMath.log2(double, RoundingMode)
  public void testRoundLog2Half() {
    // We don't expect perfect rounding accuracy.
    for (int exp : asList(-1022, -50, -1, 0, 1, 2, 3, 4, 100, 1022, 1023)) {
      for (RoundingMode mode : asList(HALF_EVEN, HALF_UP, HALF_DOWN)) {
        double x = Math.scalb(Math.sqrt(2) + 0.001, exp);

  @GwtIncompatible // TODO
  public void testSqrtExact() {
    for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
      BigInteger floor = BigIntegerMath.sqrt(x, FLOOR);
      // We only expect an exception if x was not a perfect square.
      boolean isPerfectSquare = floor.pow(2).equals(x);
      try {
        assertEquals(floor, BigIntegerMath.sqrt(x, UNNECESSARY));
        assertTrue(isPerfectSquare);
      } catch (ArithmeticException e) {

Aquí veremos un ejemplo usando [SQLModel](https://sqlmodel.tiangolo.com/).

**SQLModel** está construido sobre [SQLAlchemy](https://www.sqlalchemy.org/) y Pydantic. Fue creado por el mismo autor de **FastAPI** para ser la combinación perfecta para aplicaciones de FastAPI que necesiten usar **bases de datos SQL**.

/// tip | Consejo

    assertThat(startupTimes).hasSize(2);
    assertThat(startupTimes.get(a)).isAtLeast(150);
    // Service b startup takes at least 353 millis, but starting the timer is delayed by at least
    // 150 milliseconds. so in a perfect world the timing would be 353-150=203ms, but since either
    // of our sleep calls can be arbitrarily delayed we should just assert that there is a time
    // recorded.
    assertThat(startupTimes.get(b)).isNotNull();
  }

        assertTrue(StrictMath.pow(2.0, log2 + 1) > d);
      }
    }
  }

  @GwtIncompatible // DoubleMath.log2(double, RoundingMode)
  public void testRoundLog2Half() {
    // We don't expect perfect rounding accuracy.
    for (int exp : asList(-1022, -50, -1, 0, 1, 2, 3, 4, 100, 1022, 1023)) {
      for (RoundingMode mode : asList(HALF_EVEN, HALF_UP, HALF_DOWN)) {
        double x = Math.scalb(Math.sqrt(2) + 0.001, exp);