The value of the path parameter `item_id` will be passed to your function as the argument `item_id`.

So, if you run this example and go to [http://127.0.0.1:8000/items/foo](http://127.0.0.1:8000/items/foo), you will see a response of:

```JSON
{"item_id":"foo"}
```

## Path parameters with types { #path-parameters-with-types }

You can declare the type of a path parameter in the function, using standard Python type annotations:

   *
   * @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.

    }

    @Override
    public Iterable<Entry<String, String>> order(List<Entry<String, String>> insertionOrder) {
      return insertionOrder;
    }

    static final Function<String, String> FUNCTION =
        new Function<String, String>() {
          @Override
          public String apply(String value) {
            return Ascii.toLowerCase(value);
          }
        };

 * under the License.
 */
package org.apache.maven.internal.impl;

import java.util.Collection;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Collectors;

class CoreUtils {

    public static <T> T cast(Class<T> clazz, Object o, String name) {
        if (!clazz.isInstance(o)) {
            if (o == null) {

# Request Parameters

Here's the reference information for the request parameters.

These are the special functions that you can put in *path operation function* parameters or dependency functions with `Annotated` to get data from the request.

It includes:

* `Query()`
* `Path()`
* `Body()`
* `Cookie()`
* `Header()`
* `Form()`
* `File()`

You can import them all directly from `fastapi`:

```python

import kotlin.annotation.AnnotationTarget.CLASS
import kotlin.annotation.AnnotationTarget.CONSTRUCTOR
import kotlin.annotation.AnnotationTarget.FUNCTION

@Retention(BINARY)
@MustBeDocumented
@Target(CONSTRUCTOR, CLASS, FUNCTION)

Platform.getDeclaringClassOrNullForJ2cl = function(e) {
  return null;

   * bit(i) can alter output bit(j).
   */
  static void checkNoFunnels(HashFunction function) {
    Random rand = new Random(0);
    int keyBits = 32;
    int hashBits = function.bits();

    // output loop tests input bit
    for (int i = 0; i < keyBits; i++) {
      int same = 0x0; // bitset for output bits with same values

                function* ends, but **before** the response is sent back to the client.
                So, the dependency function will be executed **around** the *path operation
                **function***.
            * `"request"`: start the dependency before the *path operation function*
                that handles the request (similar to when using `"function"`), but end

The new [Sleep] helper function combines [time.Sleep] and [testing/synctest.Wait]....