**FastAPI** is helemaal gebaseerd op deze type hints, ze geven veel voordelen.

Maar zelfs als je **FastAPI** nooit gebruikt, heb je er baat bij om er iets over te leren.

/// note

Als je een Python expert bent en alles al weet over type hints, sla dan dit hoofdstuk over.

///

## Motivatie

Laten we beginnen met een eenvoudig voorbeeld:

```Python
{!../../docs_src/python_types/tutorial001.py!}
```

In veel gevallen is het niet direct duidelijk hoe omgevingsvariabelen nuttig zijn en hoe je ze moet toepassen. Maar ze blijven in veel verschillende scenario's opduiken als je aan het ontwikkelen bent, dus het is goed om er meer over te weten.

* **Geen brainfucks**:
    * Je hoeft geen nieuwe microtaal voor schemadefinities te leren.
    * Als je bekend bent Python types, weet je hoe je Pydantic moet gebruiken.

				if meta, err := xl.AppendTo(metaDataPoolGet()); err == nil {
					if best.reusable {
						metaDataPoolPut(best.metadata)
					}
					best.metadata = meta
					best.cached = xl
				}
			}
			toMerge = toMerge[:0]
		}
		if best.name > last {
			select {
			case <-ctxDone:
				return ctx.Err()
			case out <- *best:
				last = best.name
			}
		} else if serverDebugLog {

 * does not participate in any [interceptors][Interceptor] or [event listeners][EventListener]. It
 * doesn't include the motivating request's HTTP headers or even its full URL; only the target
 * server's hostname is sent to the proxy.
 *
 * Prior to sending any CONNECT request OkHttp always calls the proxy authenticator so that it may
 * prepare preemptive authentication. OkHttp will call [authenticate] with a fake `HTTP/1.1 407

 *
 * <h2>Prefer <a href="https://github.com/ben-manes/caffeine/wiki">Caffeine</a> over Guava's caching
 * API</h2>
 *
 * <p>The successor to Guava's caching API is <a
 * href="https://github.com/ben-manes/caffeine/wiki">Caffeine</a>. Its API is designed to make it a
 * nearly drop-in replacement. It requires Java 8+, and is not available for Android or GWT/J2CL,
 * and may have <a href="https://github.com/ben-manes/caffeine/wiki/Guava">different (usually

   * <p><b>Warning:</b> a new random seed for these functions is chosen each time the {@code
   * Hashing} class is loaded. <b>Do not use this method</b> if hash codes may escape the current
   * process in any way, for example being sent over RPC, or saved to disk. For a general-purpose,
   * non-cryptographic hash function that will never change behavior, we suggest {@link
   * #murmur3_128}.
   *

			bucket: o.Bucket,
			status: scanStateNone,
		}
	}

	// Create new and add.
	best := o.newMetacache()
	b.caches[o.ID] = best
	b.cachesRoot[best.root] = append(b.cachesRoot[best.root], best.id)
	b.updated = true
	b.debugf("returning new cache %s, bucket: %v", best.id, best.bucket)
	return best
}

// cleanup removes redundant and outdated entries.
func (b *bucketMetacache) cleanup() {

        .receivedResponseAtMillis(receivedResponseMillis)
        .build()
    }

    companion object {
      /** Synthetic response header: the local time when the request was sent. */
      private val SENT_MILLIS = "${Platform.get().getPrefix()}-Sent-Millis"

      /** Synthetic response header: the local time when the response was received. */
      private val RECEIVED_MILLIS = "${Platform.get().getPrefix()}-Received-Millis"
    }

* the data from the client to be sent through the network
* the data sent by your program to be received by the client through the network
* the contents of a file in the disk to be read by the system and given to your program