How do I integrate custom exception handling with the FastAPI exception handling?

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Your custom exception can have any custom attributes that you want. Let’s say you write it this way:

class ExceptionCustom(HTTPException):
    pass

in your custom handler, you can do something like

def exception_404_handler(request: Request, exc: HTTPException):
    return JSONResponse(status_code=status.HTTP_404_NOT_FOUND, content={"message": exc.detail})

Then, all you need to do is to raise the exception this way:

raise ExceptionCustom(status_code=404, detail="error message")

Note that you are creating a handler for this specific ExceptionCustom. If all you need is the message, you can write something more generic:

class MyHTTPException(HTTPException):
    pass

def my_http_exception_handler(request: Request, exc: HTTPException):
    return JSONResponse(status_code=exc.status_code, content={"message": exc.detail})

app.add_exception_handler(MyHTTPException, my_http_exception_handler)

This way you can raise any exception, with any status code and any message and have the message in your JSON response.

There’s a detailed explanation on FastAPI docs

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