# 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.

            <button onclick="connect(event)">Connect</button>
            <hr>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var itemId = document.getElementById("itemId")

            <button onclick="connect(event)">Connect</button>
            <hr>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var itemId = document.getElementById("itemId")

    final Map<C, V> seen = factory.get();
    final Iterator<Map<C, V>> mapIterator = backingMap.values().iterator();
    Iterator<Entry<C, V>> entryIterator = emptyIterator();

    @Override
    protected @Nullable C computeNext() {
      while (true) {
        if (entryIterator.hasNext()) {
          Entry<C, V> entry = entryIterator.next();
          if (!seen.containsKey(entry.getKey())) {

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 }

Let's start with an example **use case** and then see how to solve it with this.

	replicationMaxDataTransferRateMD = NewGaugeMD(replicationMaxDataTransferRate,
		"Maximum replication data transfer rate in bytes/sec seen since server start")
	replicationRecentBacklogCountMD = NewGaugeMD(replicationRecentBacklogCount,
		"Total number of objects seen in replication backlog in the last 5 minutes")
)

// loadClusterReplicationMetrics - `MetricsLoaderFn` for cluster replication metrics

like that curious song about the whiting!'

  `Oh, as to the whiting,' said the Mock Turtle, `they--you've
seen them, of course?'

  `Yes,' said Alice, `I've often seen them at dinn--' she
checked herself hastily.

  `I don't know where Dinn may be,' said the Mock Turtle, `but
if you've seen them so often, of course you know what they're
like.'

  `I believe so,' Alice replied thoughtfully.  `They have their

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).

# 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.

                        }
                    } catch (final Exception e) {
                        if (logger.isDebugEnabled()) {
                            logger.debug("Failed to send phase start event. phase={}, error={}", phase, e.getMessage());
                        }
                    }
                }

                @Override