sourceFilesBaseName: String,
    hashTypeSourceName: java.util.function.Function<String, String>,
    classPath: List<File>,
    classPathDependencies: List<File>,
    apiSpec: java.util.function.Function<String, Boolean>,
    parameterNamesSupplier: java.util.function.Function<String, List<String>?>,
    sinceSupplier: java.util.function.Function<String, String?>,
): List<File> =

    apiTypeProviderFor(
        asmLevel,

{!../../../docs_src/custom_response/tutorial008.py!}
```

1. This is the generator function. It's a "generator function" because it contains `yield` statements inside.
2. By using a `with` block, we make sure that the file-like object is closed after the generator function is done. So, after it finishes sending the response.

### Other utility functions

Any other utility function that you call directly can be created with normal `def` or `async def` and FastAPI won't affect the way you call it.

This is in contrast to the functions that FastAPI calls for you: *path operation functions* and dependencies.

!!! tip
    You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.
* Assign that result to the parameter in your *path operation function*.

```mermaid
graph TB

    rect rgba(0, 255, 0, .1)
        code ->> function: say_hi(name="Camila")
        function ->> execute: führe Code der Funktion aus
        execute ->> code: gib das Resultat zurück
    end

    rect rgba(0, 255, 255, .1)
        code ->> function: say_hi(name="Camila")
        function ->> code: gib das gespeicherte Resultat zurück
    end

    rect rgba(0, 255, 0, .1)

      contentType: MediaType? = null,
      contentLength: Long = -1L,
    ): ResponseBody = commonAsResponseBody(contentType, contentLength)

    @JvmStatic
    @Deprecated(
      message = "Moved to extension function. Put the 'content' argument first to fix Java",
      replaceWith =
        ReplaceWith(
          expression = "content.toResponseBody(contentType)",
          imports = ["okhttp3.ResponseBody.Companion.toResponseBody"],

    <function-class>org.codelibs.fess.taglib.FessFunctions</function-class>
    <function-signature>java.lang.String sdh(java.lang.String)</function-signature>
    <example>${fe:sdh(doc.similar_docs_hash)}</example>
  </function>

  <function>
    <description>Concatenate strings.</description>
    <name>join</name>
    <function-class>org.codelibs.fess.taglib.FessFunctions</function-class>

        }

        // Preliminary extension function check
        val extensionCandidate = couldBeExtensionFunction && ktFunction.receiverTypeReference != null &&
            method.firstParameterMatches(ktFunction.receiverTypeReference!!) &&
            ktFunction.valueParameters.size == paramCountWithReceiver
        if (!(extensionCandidate || ktFunction.valueParameters.size == paramCount)) {

# Response Model - Return Type

You can declare the type used for the response by annotating the *path operation function* **return type**.

You can use **type annotations** the same way you would for input data in function **parameters**, you can use Pydantic models, lists, dictionaries, scalar values like integers, booleans, etc.

=== "Python 3.10+"

    ```Python hl_lines="16  21"
    {!> ../../../docs_src/response_model/tutorial001_01_py310.py!}
    ```

### 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("/")`).

```Python hl_lines="7"
{!../../../docs_src/first_steps/tutorial001.py!}
```

This is a Python function.