Sprich:

```Python
q: Union[str, None] = Query(default=None)
```

... macht den Parameter optional, mit dem Defaultwert `None`, genauso wie:

```Python

```

/// tip

The second argument to <a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> is the default value to return.

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

// combined with a row-function term.
func (p *qProp) combine(q qProp) {
	switch {
	case p.err != nil:
		// Do nothing
	case q.err != nil:
		p.err = q.err
	default:
		p.isAggregation = p.isAggregation || q.isAggregation
		p.isRowFunc = p.isRowFunc || q.isRowFunc
		if p.isAggregation && p.isRowFunc {
			p.err = errNestedAggregation
		}
	}
}

# Response - Change Status Code

You probably read before that you can set a default [Response Status Code](../tutorial/response-status-code.md){.internal-link target=_blank}.

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

## Use case

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

     * list, the default property list, and its defaults, recursively, are then checked. The method returns the default
     * value argument if the property is not found.
     *
     * @param key the property key.
     * @param defaultValue a default value.
     * @return The property value of the default value
     */
    public String getProperty(String key, String defaultValue) {

	l = Config{}

	// Purge all removed keys first
	kvs := s[config.IdentityLDAPSubSys][config.Default]
	if len(kvs) > 0 {
		for _, k := range removedKeys {
			kvs.Delete(k)
		}
		s[config.IdentityLDAPSubSys][config.Default] = kvs
	}

	if err := s.CheckValidKeys(config.IdentityLDAPSubSys, removedKeys); err != nil {
		return l, err
	}

DefaultType = TypeVar("DefaultType")


def Default(value: DefaultType) -> DefaultType:
    """
    You shouldn't use this function directly.

    It's used internally to recognize when a default value has been overwritten, even
    if the overridden default value was truthy.
    """

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
public @interface Hoge {

    /**
     *
     */
    String aaa() default "123";

    /**
     *
     */
    String bbb();

    /**
     *
     */
    String ccc() default "";

# Erasure code sizing guide

## Toy Setups

Capacity constrained environments, MinIO will work but not recommended for production.

| servers | drives (per node) | stripe_size | parity chosen (default) | tolerance for reads (servers) | tolerance for writes (servers) |
|--------:|------------------:|------------:|------------------------:|------------------------------:|-------------------------------:|

///

## Die Default-Exceptionhandler überschreiben

**FastAPI** hat einige Default-Exceptionhandler.

Diese Handler kümmern sich darum, Default-JSON-Responses zurückzugeben, wenn Sie eine `HTTPException` `raise`n, und wenn der Request ungültige Daten enthält.