[Solved] Why does this custom validation error handler fail to catch errors? ```python from fastapi import FastAPI from fastapi.... Why does this custom validation error handler fail to catch errors? | FastAPI

FastAPI - Error Handling

Why does this custom validation error handler fail to catch errors? ```python from fastapi import FastAPI from fastapi.exceptions import ValidationError from fastapi.responses import JSONResponse app = FastAPI() @app.exception_handler(ValidationError) async def custom_handler(request, exc): return JSONResponse(status_code=422, content={'detail': 'Custom error'}) ```

AJSONResponse is not suitable for error responses

BThe handler must be synchronous, not async

CIt should catch RequestValidationError, not ValidationError

DThe exception handler decorator is missing parentheses

Step-by-Step Solution

Solution:

Step 1: Identify the correct exception for FastAPI validation errors
FastAPI raises RequestValidationError, not ValidationError, for request validation issues.
Step 2: Understand why the handler does not catch errors
Because the handler listens for ValidationError, it misses RequestValidationError exceptions.
Final Answer:
It should catch RequestValidationError, not ValidationError -> Option C
Quick Check:
Use RequestValidationError to catch validation errors [OK]

Quick Trick: Catch RequestValidationError, not ValidationError, for FastAPI validation [OK]

Common Mistakes:

MISTAKES

Using ValidationError instead of RequestValidationError
Thinking async handlers are invalid
Misusing JSONResponse for error handling

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Why does this custom validation error handler fail to catch errors?

Step 1: Identify the correct exception for FastAPI validation errors

Step 2: Understand why the handler does not catch errors

Final Answer:

Quick Check:

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