Without a data validation system, you would have to do all the checks by hand, in code.

These features are what Marshmallow was built to provide. It is a great library, and I have used it a lot before.

As part of that, I needed to investigate, test and use many alternatives.

The history of **FastAPI** is in great part the history of its predecessors.

As said in the section [Alternatives](alternatives.md){.internal-link target=_blank}:

<blockquote markdown="1">

**FastAPI** wouldn't exist if not for the previous work of others.

/**
 * A utility for testing an Iterator implementation by comparing its behavior to that of a "known
 * good" reference implementation. In order to accomplish this, it's important to test a great
 * variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link
 * Iterator#remove} operations. This utility takes the brute-force approach of trying <i>all</i>

/**
 * A utility for testing an Iterator implementation by comparing its behavior to that of a "known
 * good" reference implementation. In order to accomplish this, it's important to test a great
 * variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link
 * Iterator#remove} operations. This utility takes the brute-force approach of trying <i>all</i>

@Tag("Slowish")
class RelayTest {
  @TempDir
  var tempDir: File? = null
  private val executor = Executors.newCachedThreadPool(threadFactory("RelayTest"))
  private val metadata: ByteString = "great metadata!".encodeUtf8()
  private lateinit var file: File

  @BeforeEach
  fun setUp() {
    file = File(tempDir, "test")
  }

  @AfterEach
  fun tearDown() {
    executor.shutdown()
  }

       * crashes on Android when running in 32-bit mode. For maximum safety, we shouldn't use
       * Unsafe.getLong() at all, but the performance benefit on x86_64 is too great to ignore, so
       * as a compromise, we enable the optimization only on platforms that we specifically know to
       * work.
       *

Up to now, you have been using common data types, like:

* `int`
* `float`
* `str`
* `bool`

But you can also use more complex data types.

And you will still have the same features as seen up to now:

* Great editor support.
* Data conversion from incoming requests.
* Data conversion for response data.
* Data validation.
* Automatic annotation and documentation.

## Other data types

_2020-07-11_

 *  New: Change `HeldCertificate.Builder` to use its own ASN.1 certificate encoder. This is part
    of our effort to remove the okhttp-tls module's dependency on Bouncy Castle. We think Bouncy
    Castle is great! But it's a large dependency (6.5 MiB) and its security provider feature
    impacts VM-wide behavior.

 *  New: Reduce contention for applications that make a very high number of concurrent requests.

<img src="/img/tutorial/security/image02.png">

!!! note
    It doesn't matter what you type in the form, it won't work yet. But we'll get there.

This is of course not the frontend for the final users, but it's a great automatic tool to document interactively all your API.

It can be used by the frontend team (that can also be yourself).

It can be used by third party applications and systems.

So, the thief won't be able to try to use that password in another system (as many users use the same password everywhere, this would be dangerous).

## Install `passlib`

PassLib is a great Python package to handle password hashes.

It supports many secure hashing algorithms and utilities to work with them.

The recommended algorithm is "Bcrypt".

So, install PassLib with Bcrypt:

<div class="termy">