# Response - Change Status Code { #response-change-status-code }

You probably read before that you can set a default [Response Status Code](../tutorial/response-status-code.md).

But in some cases you need to return a different status code than the default.

## Use case { #use-case }

For example, imagine that you want to return an HTTP status code of "OK" `200` by default.

            }
        """

        when:
        def result = gradleRunner("test", '-Dtests.seed=default', '-Pfoo=bar').build()

        then:
        result.task(':test').outcome == TaskOutcome.SUCCESS

        when:
        result = gradleRunner("test", '-i', '-Dtests.seed=default', '-Pfoo=baz').build()

        then:
        result.task(':test').outcome == TaskOutcome.UP_TO_DATE
    }

This can be very useful for setting up **resources** that you need to use for the whole app, and that are **shared** among requests, and/or that you need to **clean up** afterwards. For example, a database connection pool, or loading a shared machine learning model.

## Use Case { #use-case }

  }

  public void testParanoidHashBytes() {
    HashFn hf =
        new HashFn() {
          @Override
          public byte[] hash(byte[] input, int seed) {
            return murmur3_32(seed).hashBytes(input).asBytes();
          }
        };
    // Murmur3A, MurmurHash3 for x86, 32-bit (MurmurHash3_x86_32)
    // https://github.com/aappleby/smhasher/blob/master/src/main.cpp

    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <!--
    Some tests need reflective access to the internals of these packages. It is only the
    tests themselves and not the code being tested that needs that access, though there's no
    obvious way to ensure that.

    We could consider arranging things so that only the tests we know need this would get
    the add-opens. Right now that doesn't seem worth the effort, though.

# Security Tools

When you need to declare dependencies with OAuth2 scopes you use `Security()`.

But you still need to define what is the dependable, the callable that you pass as a parameter to `Depends()` or `Security()`.

There are multiple tools that you can use to create those dependables, and they get integrated into OpenAPI so they are shown in the automatic docs UI, they can be used by automatically generated clients and SDKs, etc.

a <dfn title="A utility/system to store computed/generated values, to reuse them instead of computing them again.">"cache"</dfn> and pass it to all the "dependants" that need it in that specific request, instead of calling the dependency multiple times for the same request.

In an advanced scenario where you know you need the dependency to be called at every step (possibly multiple times) in the same request instead of using the "cached" value, you can set the parameter `use_cache=False` when...

{* ../../docs_src/query_params_str_validations/tutorial002_py310.py hl[7] *}

As in this case (without using `Annotated`) we have to replace the default value `None` in the function with `Query()`, we now need to set the default value with the parameter `Query(default=None)`, it serves the same purpose of defining that default value (at least for FastAPI).

So:

```Python
q: str | None = Query(default=None)
```

Do you want to understand what's all that above?

Continue reading. 👇🤓

///

## Why Virtual Environments { #why-virtual-environments }

To work with FastAPI you need to install [Python](https://www.python.org/).

After that, you would need to **install** FastAPI and any other **packages** you want to use.

To install packages you would normally use the `pip` command that comes with Python (or similar alternatives).

### Short { #short }

It has sensible **defaults** for everything, with optional configurations everywhere. All the parameters can be fine-tuned to do what you need and to define the API you need.

But by default, it all **"just works"**.

### Validation { #validation }

* Validation for most (or all?) Python **data types**, including:
    * JSON objects (`dict`).