private final LittleEndianDataOutputStream out = new LittleEndianDataOutputStream(baos);

  public void testWriteLittleEndian() throws IOException {

    /* Write out various test values in LITTLE ENDIAN FORMAT */
    out.write(new byte[] {-100, 100});
    out.writeBoolean(true);
    out.writeBoolean(false);
    out.writeByte(100);
    out.writeByte(-100);
    out.writeByte((byte) 200);
    out.writeChar('a');

  private final LittleEndianDataOutputStream out = new LittleEndianDataOutputStream(baos);

  public void testWriteLittleEndian() throws IOException {

    /* Write out various test values in LITTLE ENDIAN FORMAT */
    out.write(new byte[] {-100, 100});
    out.writeBoolean(true);
    out.writeBoolean(false);
    out.writeByte(100);
    out.writeByte(-100);
    out.writeByte((byte) 200);
    out.writeChar('a');

  }

  public void testReadLittleEndian() throws IOException {
    DataInput in = new LittleEndianDataInputStream(new ByteArrayInputStream(data));

    /* Read in various values in LITTLE ENDIAN FORMAT */
    byte[] b = new byte[2];
    in.readFully(b);
    assertEquals(-100, b[0]);
    assertEquals(100, b[1]);
    assertEquals(true, in.readBoolean());
    assertEquals(false, in.readBoolean());

   * compatible pure-Java fallback.
   */
  private static final LittleEndianBytes byteArray = makeGetter();

  /**
   * Load 8 bytes into long in a little endian manner, from the substring between position and
   * position + 8. The array must have at least 8 bytes from offset (inclusive).
   *
   * @param input the input bytes

Some time ago, [a **FastAPI** user asked](https://github.com/fastapi/fastapi/issues/3#issuecomment-454956920):

> What’s the history of this project? It seems to have come from nowhere to awesome in a few weeks [...]

Here's a little bit of that history.

## Alternatives { #alternatives }

FastAPI version 0.119.0 introduced partial support for Pydantic v1 from inside of Pydantic v2 (as `pydantic.v1`), to facilitate the migration to v2.

FastAPI 0.126.0 dropped support for Pydantic v1, while still supporting `pydantic.v1` for a little while.

/// warning

The Pydantic team stopped support for Pydantic v1 for the latest versions of Python, starting with **Python 3.14**.

This includes `pydantic.v1`, which is no longer supported in Python 3.14 and above.

You could use that command for example to start your **FastAPI** app in a container, in a server, etc.

## ASGI Servers { #asgi-servers }

Let's go a little deeper into the details.

FastAPI uses a standard for building Python web frameworks and servers called <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr>. FastAPI is an ASGI web framework.

    public boolean cancel(boolean mayInterruptIfRunning) {
      throw new AssertionFailedError();
    }

    @Override
    public V get() throws InterruptedException {
      /*
       * Wait a little to give us time to call addListener before the future's
       * value is set in addition to the call we'll make after then.
       */
      allowGetToComplete.await(1, SECONDS);

    public boolean cancel(boolean mayInterruptIfRunning) {
      throw new AssertionFailedError();
    }

    @Override
    public V get() throws InterruptedException {
      /*
       * Wait a little to give us time to call addListener before the future's
       * value is set in addition to the call we'll make after then.
       */
      allowGetToComplete.await(1, SECONDS);

}

.screenshot:before {
  content: '';
  position: absolute;
  top: 15px;
  left: 15px;
  display: inline-block;
  width: 15px;
  height: 15px;
  border-radius: 50%;
  /* A little hack to display the window buttons in one pseudo element. */
  background: #d9515d;
  -webkit-box-shadow: 25px 0 0 #f4c025, 50px 0 0 #3ec930;
          box-shadow: 25px 0 0 #f4c025, 50px 0 0 #3ec930;
}