<div style="text-align: left; direction: ltr;">"We've switched over to <strong>FastAPI</strong> for our <strong>APIs</strong> [...] I think you'll like it [...]"</div>

"_Nous sommes passés à **FastAPI** pour nos **APIs** [...] Je pense que vous l'aimerez [...]_"

---

"_如果您想學習一種用於構建 REST API 的**現代框架**，不能錯過 **FastAPI** [...] 它非常快速、且易於使用和學習 [...]_"

"_我們的 **APIs** 已經改用 **FastAPI** [...] 我想你會喜歡它 [...]_"

"_We've switched over to **FastAPI** for our **APIs** [...] I think you'll like it [...]_"

        #        ; tableExceptList=list:{FOO_TABLE ; prefix:FOO_ ; suffix:_FOO ; contain:_FOO_}
        #        ; tableTargetList=list:{FOO_TABLE ; prefix:FOO_ ; suffix:_FOO ; contain:_FOO_}
        #        ; columnExceptMap=map:{
        #            ; FOO_TABLE = list:{FOO_COLUMN ; prefix:FOO_ ; suffix:_FOO ; contain:_FOO_}
        #        }
        #        ; isSuppressCommonColumn=false

      BiMap<V, K> inv = getMap().inverse();
      assertFalse(
          "Inverse should not contain entry " + reversed, inv.entrySet().contains(reversed));
      assertFalse(
          "Inverse should not contain key " + reversed.getKey(),
          inv.containsKey(reversed.getKey()));
      assertFalse(
          "Inverse should not contain value " + reversed.getValue(),
          inv.containsValue(reversed.getValue()));
      /*

var bufLength = payloadLenForMsgLen(maxRecordMessageLength)

// newRecordsMessage - creates new Records Message which can contain a single record, partial records,
// or multiple records. Depending on the size of the result, a response can contain one or more of these messages.
//
// Header specification
// Records messages contain three headers, as follows:
// https://docs.aws.amazon.com/AmazonS3/latest/API/images/s3select-frame-diagram-record.png
//

  }

  protected void expectMissingKeys(K... elements) {
    for (K element : elements) {
      assertFalse("Should not contain key " + element, getMap().containsKey(element));
    }
  }

  protected void expectMissingValues(V... elements) {
    for (V element : elements) {
      assertFalse("Should not contain value " + element, getMap().containsValue(element));
    }
  }

    assertThrows(NullPointerException.class, () -> getMap().putIfAbsent(null, v3()));
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported putIfAbsent(null, value)");
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUES)
  public void testPutIfAbsent_nullValueUnsupportedAndKeyAbsent() {

## The normal **FastAPI** app

Let's first see how the normal API app would look like before adding the callback.

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../docs_src/openapi_callbacks/tutorial001.py!}
```

/// tip