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```Python hl_lines="1  13"
{!../../docs_src/events/tutorial003.py!}
```

Ein **Kontextmanager** in Python ist etwas, das Sie in einer `with`-Anweisung verwenden können, zum Beispiel kann `open()` als Kontextmanager verwendet werden:

```Python
with open("file.txt") as file:
    file.read()
```

In neueren Versionen von Python gibt es auch einen **asynchronen Kontextmanager**. Sie würden ihn mit `async with` verwenden:

```Python

			configDumpFile, err := os.Open(fmt.Sprintf("testdata/secret/%s/config_dump.json", tc.sds))
			if err != nil {
				t.Errorf("error opening test data file: %v", err)
			}
			defer configDumpFile.Close()
			configDump, err := io.ReadAll(configDumpFile)
			if err != nil {
				t.Errorf("error reading test data file: %v", err)
			}

			outFile, err := os.Open(fmt.Sprintf("testdata/secret/%s/output", tc.sds))

			content []byte
		}
		files := []file{}

		for _, f := range r.File {
			fr, err := f.Open()
			if err != nil {
				continue
			}
			content, err := io.ReadAll(fr)
			if err != nil {
				continue
			}
			files = append(files, file{header: &f.FileHeader, content: content})
			if _, err := r.Open(f.Name); err != nil {
				continue
			}
		}

    patha = tmp_path / "test.txt"
    pathb = tmp_path / "testb.txt"
    patha.write_text("<file content>")
    pathb.write_text("<file b content>")

    client = TestClient(app)
    with patha.open("rb") as filea, pathb.open("rb") as fileb:
        response = client.post(
            "/files/",
            data={"token": "foo"},
            files={"file": filea, "fileb": ("testb.txt", fileb, "text/plain")},
        )

@SuppressSignatureCheck
sealed class ConnectionEvent {
  abstract val timestampNs: Long
  open val connection: Connection?
    get() = null

  /** Returns if the event closes this event, or null if this is no open event. */
  open fun closes(event: ConnectionEvent): Boolean? = null

  val name: String
    get() = javaClass.simpleName

  data class ConnectStart(

    Platform.get().log("[WS $name] onOpen", Platform.INFO, null)
    val delegate = delegate
    if (delegate != null) {
      this.delegate = null
      delegate.onOpen(webSocket, response)
    } else {
      events.add(Open(webSocket, response))
    }
  }

  override fun onMessage(
    webSocket: WebSocket,
    bytes: ByteString,
  ) {
    Platform.get().log("[WS $name] onMessage", Platform.INFO, null)
    val delegate = delegate

      for (int j = i + 1; j <= MAX_BOUND; j++) {
        for (BoundType lowerType : BoundType.values()) {
          for (BoundType upperType : BoundType.values()) {
            if (i == j & lowerType == OPEN & upperType == OPEN) {
              continue;
            }
            builder.add(Range.range(i, lowerType, j, upperType));
          }
        }
      }
    }
    RANGES = builder.build();
  }

def test_custom_middleware_exception(tmp_path: Path):
    default_pydantic_max_size = 2**16
    path = tmp_path / "test.txt"
    path.write_bytes(b"x" * (default_pydantic_max_size + 1))

    with client:
        with open(path, "rb") as file:
            response = client.post("/middleware", files={"file": file})
        assert response.status_code == 422, response.text
        assert response.json() == {
            "detail": {

      for (int j = i + 1; j <= MAX_BOUND; j++) {
        for (BoundType lowerType : BoundType.values()) {
          for (BoundType upperType : BoundType.values()) {
            if (i == j & lowerType == OPEN & upperType == OPEN) {
              continue;
            }
            builder.add(Range.range(i, lowerType, j, upperType));
          }
        }
      }
    }
    RANGES = builder.build();
  }