{* ../../docs_src/first_steps/tutorial001.py hl[3] *}

Here the `app` variable will be an "instance" of the class `FastAPI`.

This will be the main point of interaction to create all your API.

### Step 3: create a *path operation* { #step-3-create-a-path-operation }

#### Path { #path }

"Path" here refers to the last part of the URL starting from the first `/`.

So, in a URL like:

There are many posts, articles, tools, and projects, related to **FastAPI**.

Here's an incomplete list of some of them.

/// tip

If you have an article, project, tool, or anything related to **FastAPI** that is not yet listed here, create a <a href="https://github.com/fastapi/fastapi/edit/master/docs/en/data/external_links.yml" class="external-link" target="_blank">Pull Request adding it</a>.

///

    /*
     * Since we use AtomicReferenceFieldUpdaterAtomicHelper by default, we'll "obviously" use it
     * even when Unsafe isn't available. But it's nice to have a check here to make sure that
     * nothing somehow goes wrong as the JDK restricts access to Unsafe.
     */
    checkHelperVersion(NO_UNSAFE, "AtomicReferenceFieldUpdaterAtomicHelper");
    /*

    // contract to guarantee ordering among runnables we'd have to modify the logic here to allow
    // it.
    executeListener(runnable, executor);
  }

  /**
   * Runs this execution list, executing all existing pairs in the order they were added. However,
   * note that listeners added after this point may be executed before those previously added, and

Então, se você rodar este exemplo e for até <a href="http://127.0.0.1:8000/items/foo" class="external-link" target="_blank">http://127.0.0.1:8000/items/foo</a>, você verá a seguinte resposta:

```JSON
{"item_id":"foo"}
```

## Parâmetros da rota com tipos

Você pode declarar o tipo de um parâmetro na função usando as anotações padrões do Python:

If not provided, it's `None` by default, here we provide `"World"` as the default value to use.

///

Then you could call that Python program:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console
// Here we don't set the env var yet
$ python main.py

// As we didn't set the env var, we get the default value

Você verá a documentação automática da API para a aplicação principal, incluindo apenas suas próprias _operações de rota_:

<img src="/img/tutorial/sub-applications/image01.png">

E então, abra a documentação para a sub-aplicação, em <a href="http://127.0.0.1:8000/subapi/docs" class="external-link" target="_blank">http://127.0.0.1:8000/subapi/docs</a>.

     * For direct buffers, we rely on GC. A more sophisticated
     * implementation could maintain a buffer pool here as well.
     *
     * @param buffer buffer to release
     */
    public void releaseBuffer(ByteBuffer buffer) {
        // For direct buffers, we rely on GC
        // Could implement a more sophisticated buffer pool here
    }

    /**
     * Clean up all pooled regions
     *

      // should never reach here!
      throw new UnsupportedOperationException();
    }

    @Override
    public Entry<K, V> belowSamplesGreater() {
      // should never reach here!
      throw new UnsupportedOperationException();
    }

    @Override
    public Entry<K, V> aboveSamplesLesser() {
      // should never reach here!
      throw new UnsupportedOperationException();
    }

```

</div>

////

The only new option here is `--workers` telling Uvicorn to start 4 worker processes.

You can also see that it shows the **PID** of each process, `27365` for the parent process (this is the **process manager**) and one for each worker process: `27368`, `27369`, `27370`, and `27367`.

## Deployment Concepts { #deployment-concepts }