from fastapi import Depends, FastAPI, HTTPException
from fastapi.exceptions import RequestValidationError
from fastapi.testclient import TestClient
from starlette.responses import JSONResponse


def http_exception_handler(request, exception):
    return JSONResponse({"exception": "http-exception"})


def request_validation_exception_handler(request, exception):
    return JSONResponse({"exception": "request-validation"})

{* ../../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] *}

        )
    return {"item": items[item_id]}


@app.get("/http-no-body-statuscode-exception")
async def no_body_status_code_exception():
    raise HTTPException(status_code=204)


@app.get("/http-no-body-statuscode-with-detail-exception")
async def no_body_status_code_with_detail_exception():
    raise HTTPException(status_code=204, detail="I should just disappear!")


@app.get("/starlette-items/{item_id}")

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,

 * </li>
 * <li>child exception summaries.</li>
 * </ul>
 */
public class ExceptionSummary {

    private Throwable exception;

    private String message;

    private String reference;

    private List<ExceptionSummary> children;

    public ExceptionSummary(Throwable exception, String message, String reference) {
        this(exception, message, reference, null);
    }