///

### Step 4: define the **path operation function** { #step-4-define-the-path-operation-function }

This is our "**path operation function**":

* **path**: is `/`.
* **operation**: is `get`.
* **function**: is the function below the "decorator" (below `@app.get("/")`).

{* ../../docs_src/first_steps/tutorial001_py310.py hl[7] *}

This is a Python function.

import org.gradle.api.tasks.util.PatternSet;
import org.gradle.internal.Factory;

import javax.inject.Inject;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.util.function.Function;
import java.util.stream.Collectors;

import static org.elasticsearch.gradle.util.GradleUtils.getProjectPathFromTask;

/**

      extends AbstractSequentialList<T> implements Serializable {
    final List<F> fromList;
    final Function<? super F, ? extends T> function;

    TransformingSequentialList(List<F> fromList, Function<? super F, ? extends T> function) {
      this.fromList = checkNotNull(fromList);
      this.function = checkNotNull(function);
    }

    /**

public class MapComputeIfAbsentTester<K, V> extends AbstractMapTester<K, V> {

  @MapFeature.Require(SUPPORTS_PUT)
  public void testComputeIfAbsent_supportedAbsent() {
    assertEquals(
        "computeIfAbsent(notPresent, function) should return new value",
        v3(),
        getMap()
            .computeIfAbsent(
                k3(),
                k -> {
                  assertEquals(k3(), k);
                  return v3();

  private static final String RESULT_DATA = "SUCCESS";

  private SettableFuture<String> outputFuture;
  // Signals that the function is waiting to complete
  private CountDownLatch funcIsWaitingLatch;
  // Signals the function so it will complete
  private CountDownLatch funcCompletionLatch;

  @Override
  protected ListenableFuture<String> buildChainingFuture(ListenableFuture<Integer> inputFuture) {

  private static final String RESULT_DATA = "SUCCESS";

  private SettableFuture<String> outputFuture;
  // Signals that the function is waiting to complete
  private CountDownLatch funcIsWaitingLatch;
  // Signals the function so it will complete
  private CountDownLatch funcCompletionLatch;

  @Override
  protected ListenableFuture<String> buildChainingFuture(ListenableFuture<Integer> inputFuture) {

///

## Create a middleware { #create-a-middleware }

To create a middleware you use the decorator `@app.middleware("http")` on top of a function.

The middleware function receives:

* The `request`.
* A function `call_next` that will receive the `request` as a parameter.
    * This function will pass the `request` to the corresponding *path operation*.
    * Then it returns the `response` generated by the corresponding *path operation*.

public class MapComputeIfAbsentTester<K, V> extends AbstractMapTester<K, V> {

  @MapFeature.Require(SUPPORTS_PUT)
  public void testComputeIfAbsent_supportedAbsent() {
    assertEquals(
        "computeIfAbsent(notPresent, function) should return new value",
        v3(),
        getMap()
            .computeIfAbsent(
                k3(),
                k -> {
                  assertEquals(k3(), k);
                  return v3();

            ws.onmessage = function(event) {
                var messages = document.getElementById('messages')
                var message = document.createElement('li')
                var content = document.createTextNode(event.data)
                message.appendChild(content)
                messages.appendChild(message)
            };
            function sendMessage(event) {

///

## Use the model { #use-the-model }

Inside of the function, you can access all the attributes of the model object directly:

{* ../../docs_src/body/tutorial002_py310.py *}

## Request body + path parameters { #request-body-path-parameters }

You can declare path parameters and request body at the same time.