{* ../../docs_src/handling_errors/tutorial002_py39.py hl[14] *}

## Install custom exception handlers { #install-custom-exception-handlers }

You can add custom exception handlers with <a href="https://www.starlette.dev/exceptions/" class="external-link" target="_blank">the same exception utilities from Starlette</a>.

Let's say you have a custom exception `UnicornException` that you (or a library you use) might `raise`.

    captured_exception.exception = None
    try:
        client.get("/items/")
    except Exception:
        pass

    assert captured_exception.exception is not None
    error_str = str(captured_exception.exception)
    assert "get_item" in error_str
    assert "/items/" in error_str


def test_websocket_validation_error_includes_endpoint_context():
    captured_exception.exception = None
    try:

from pydantic import BaseModel, create_model
from starlette.exceptions import HTTPException as StarletteHTTPException
from starlette.exceptions import WebSocketException as StarletteWebSocketException


class EndpointContext(TypedDict, total=False):
    function: str
    path: str
    file: str
    line: int


class HTTPException(StarletteHTTPException):
    """
    An HTTP exception you can raise in your own code to show errors to the client.

Wenn Sie eine Exception in einer Abhängigkeit mit `yield` abfangen, sollten Sie – sofern Sie nicht eine andere `HTTPException` oder Ähnliches auslösen – **die ursprüngliche Exception erneut auslösen**.

Sie können dieselbe Exception mit `raise` erneut auslösen:

{* ../../docs_src/dependencies/tutorial008d_an_py39.py hl[17] *}

If you use a `try` block in a dependency with `yield`, you'll receive any exception that was thrown when using the dependency.

For example, if some code at some point in the middle, in another dependency or in a *path operation*, made a database transaction "rollback" or created any other exception, you would receive the exception in your dependency.

So, you can look for that specific exception inside the dependency with `except SomeException`.

    private Model read(String pom) throws Exception {
        String resource = "/poms/validation/" + pom;
        try (InputStream is = getClass().getResourceAsStream(resource)) {
            assertNotNull(is, "missing resource: " + resource);
            return new Model(new MavenStaxReader().read(is));
        }
    }

    private SimpleProblemCollector validate(String pom) throws Exception {

     * @param exception The exception that caused this problem, may be {@code null}.
     */
    // mkleint: does this need to be public?
    public DefaultModelProblem(
            String message,
            Severity severity,
            Version version,
            Model source,
            int lineNumber,
            int columnNumber,
            Exception exception) {
        this(
                message,

        Exception e = assertThrows(Exception.class, () -> ee.evaluate("${session.rootDirectory}"));
        e = assertInstanceOf(IntrospectionException.class, e.getCause());
        e = assertInstanceOf(IllegalStateException.class, e.getCause());
        assertEquals(RootLocator.UNABLE_TO_FIND_ROOT_PROJECT_MESSAGE, e.getMessage());
    }

    @Test
    void testRootDirectory() throws Exception {

        String reference = "";
        if (!dejaVu.add(exception)) {
            return reference;
        }

        if (exception != null) {
            if (exception instanceof MojoExecutionException) {
                reference = MojoExecutionException.class.getSimpleName();

                Throwable cause = exception.getCause();

            List<Exception> exceptions = result.getResolutionErrors(dependency);
            for (Exception e : exceptions) {
                msg.append("\t").append(e.getMessage()).append(System.lineSeparator());
            }
        }

        for (Exception exception : result.getCollectionErrors()) {
            msg.append(exception.getMessage()).append(System.lineSeparator());