{* ../../docs_src/authentication_error_status_code/tutorial001_an_py39.py hl[9:13] *}

/// tip

Notice that the function returns the exception instance, it doesn't raise it. The raising is done in the rest of the internal code.

  }

  // enum singleton pattern
  private enum TrimStringFunction implements Function<String, String> {
    INSTANCE;

    @Override
    public String apply(String string) {
      return whitespace().trimFrom(string);
    }
  }

  public void testCompose() {
    Function<String, String> trim = TrimStringFunction.INSTANCE;
    Predicate<String> equalsFoo = Predicates.equalTo("Foo");

# Dependencies - `Depends()` and `Security()`

## `Depends()`

Dependencies are handled mainly with the special function `Depends()` that takes a callable.

Here is the reference for it and its parameters.

You can import it directly from `fastapi`:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

    /**
     * Pipe operations should behave like the <code>CallNamedPipe</code> Win32 Named Pipe function.
     */

    public static final int PIPE_TYPE_CALL = 0x0100;

    /**
     * Pipe operations should behave like the <code>TransactNamedPipe</code> Win32 Named Pipe function.
     */

    public static final int PIPE_TYPE_TRANSACT = 0x0200;

    /**

   *
   * @throws NullPointerException if the function returns {@code null}
   * @since 12.0
   */
  public abstract <V> Optional<V> transform(Function<? super T, V> function);

  /**
   * Returns {@code true} if {@code object} is an {@code Optional} instance, and either the
   * contained references are {@linkplain Object#equals equal} to each other or both are absent.

import java.io.Serializable;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import java.util.function.ToIntFunction;
import java.util.stream.Collector;
import org.jspecify.annotations.Nullable;

/**
 * A {@link Multiset} whose contents will never change, with many other important properties

			mod = result.module;
			inst = result.instance;
			document.getElementById("runButton").disabled = false;
		}).catch((err) => {
			console.error(err);
		});

		async function run() {
			console.clear();
			await go.run(inst);
			inst = await WebAssembly.instantiate(mod, go.importObject); // reset instance
		}
	</script>

	<button onClick="run();" id="runButton" disabled>Run</button>

	for ok && file != "" {
		// Clean up the common prefixes
		file = trimTrace(file)
		// Get the function name
		_, funcName := filepath.Split(runtime.FuncForPC(pc).Name())
		// Skip duplicate traces that start with file name, "<autogenerated>"
		// and also skip traces with function name that starts with "runtime."
		if !strings.HasPrefix(file, "<autogenerated>") &&
			!strings.HasPrefix(funcName, "runtime.") {

8. Notice that this *path operation function* uses regular `def` instead of `async def`.

    As always, in FastAPI you can combine `def` and `async def` as needed.

    If you need a refresher about when to use which, check out the section _"In a hurry?"_ in the docs about [`async` and `await`](../async.md#in-a-hurry){.internal-link target=_blank}.

  private static final List<String> SOME_STRING_LIST = asList("1", "2", "3", "4");

  private static final Function<Number, String> SOME_FUNCTION = new SomeFunction();

  private static class SomeFunction implements Function<Number, String>, Serializable {
    @Override
    public String apply(Number n) {
      return String.valueOf(n);
    }