How to setup different exception_handler's for different routes or http_handlers?

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Example Code

from fastapi import FastAPI

app = FastAPI()


@app.exception_handler(RequestValidationError)
async def validation_exception(request, exc):
    return Response(
        content='Incorrect symbol',
        media_type="text/html",
        status_code=404
    )


@app.get('/')
def foo(q: str = Query(regex='^[0-9]+$')):
   pass

@app.post('/')
def bar(q: str = Query(regex='^[0-9]+$')):
    pass

Description

I can add @app.exception_handler(RequestValidationError) for all Validation Errors like in code above. How to add different exception_handler’s to get (foo()) and post (bar()) handlers with same regex validation?

from fastapi import FastAPI

app = FastAPI()

@app.get('/')
def foo(q: str = Query(regex='^[0-9]+$')):
   pass

@app.post('/')
def bar(q: str = Query(regex='^[0-9]+$')):
    pass

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.85.1

Python Version

3.10

Additional Context

No response

[yinziyan1206]

use different app, and mount it on main app. Its a basic usage in starlette

[JarroVGIT]

Well, out of the box you can’t have different exception handlers for the same Exception subtype. That is because the exception handlers are registered at the upmost app level.

One way of dealing with your requirement is to create a dependency function that takes the parameter as its parameter, but without the regex. This logic would then be moved to the function itself, and based on the request method you could raise a specific Exception. But that becomes unwieldy if your real-life code is a bit more complex than the example you gave (which I assume it is).

On the other hand (and this is not helping you at all, I realise) you could argue that an error response from an API framework in the form of html is… sketchy and should be JSON in the first place?