Python FastAPIのエラーハンドリング：堅牢なカスタム例外ハンドラーの構築

            \nclass OutOfStockError(Exception):\n    def __init__(self, product_id: int):\n        self.product_id = product_id\n        self.message = f"Product with ID {product_id} is out of stock."\n
            

              
                Copy
              
            
          

            \nfrom fastapi import FastAPI, Request, HTTPException\nfrom fastapi.responses import JSONResponse\n\napp = FastAPI()\n\nclass OutOfStockError(Exception):\n    def __init__(self, product_id: int):\n        self.product_id = product_id\n        self.message = f"Product with ID {product_id} is out of stock."\n\n@app.exception_handler(OutOfStockError)\nasync def out_of_stock_exception_handler(request: Request, exc: OutOfStockError):\n    return JSONResponse(\n        status_code=400,\n        content={"message": exc.message},\n    )\n\n@app.get("/products/{product_id}")\nasync def get_product(product_id: int):\n    # Simulate checking product stock\n    if product_id == 123:\n        raise OutOfStockError(product_id=product_id)\n    return {"product_id": product_id, "name": "Example Product", "price": 29.99}\n
            

              
                Copy
              
            
          

            \nfrom fastapi import FastAPI, Request\nfrom fastapi.responses import JSONResponse\n\napp = FastAPI()\n\n@app.exception_handler(ValueError)\nasync def value_error_exception_handler(request: Request, exc: ValueError):\n    return JSONResponse(\n        status_code=400,\n        content={"message": str(exc)},\n    )\n\n@app.get("/items/{item_id}")\nasync def get_item(item_id: int):\n    # Simulate invalid item_id\n    if item_id < 0:\n        raise ValueError("Item ID must be a positive integer.")\n    return {"item_id": item_id, "name": "Example Item"}\n
            

              
                Copy
              
            
          

            \nfrom fastapi import FastAPI, HTTPException\n\napp = FastAPI()\n\n@app.get("/users/{user_id}")\nasync def get_user(user_id: int):\n    # Simulate user not found\n    if user_id == 999:\n        raise HTTPException(status_code=404, detail="User not found")\n    return {"user_id": user_id, "name": "Example User"}\n
            

              
                Copy
              
            
          

            \nfrom fastapi import FastAPI, Request\nfrom fastapi.responses import JSONResponse\nimport logging\n\napp = FastAPI()\n\nlogger = logging.getLogger(__name__)\n\n@app.exception_handler(Exception)\nasync def global_exception_handler(request: Request, exc: Exception):\n    logger.exception(f"Unhandled exception: {exc}")\n    return JSONResponse(\n        status_code=500,\n        content={"message": "Internal server error"},\n    )\n\n@app.get("/error")\nasync def trigger_error():\n    raise ValueError("This is a test error.")\n
            

              
                Copy
              
            
          

            \nfrom fastapi import FastAPI, Request\nfrom fastapi.responses import JSONResponse\nimport logging\n\napp = FastAPI()\n\nlogger = logging.getLogger(__name__)\n\n@app.middleware("http")\nasync def exception_middleware(request: Request, call_next):\n    try:\n        response = await call_next(request)\n    except Exception as exc:\n        logger.exception(f"Unhandled exception: {exc}")\n        return JSONResponse(\n            status_code=500,\n            content={"message": "Internal server error"},\n        )\n    return response\n\n@app.get("/error")\nasync def trigger_error():\n    raise ValueError("This is a test error.")\n
            

              
                Copy
              
            
          

            \nfrom fastapi import FastAPI, Request, HTTPException\nfrom fastapi.responses import JSONResponse\nfrom typing import Dict\n\napp = FastAPI()\n\n# Mock translation dictionary (replace with a real i18n library)\ntranslations: Dict[str, Dict[str, str]] = {\n    "en": {\n        "product_not_found": "Product with ID {product_id} not found.",\n        "invalid_input": "Invalid input: {error_message}",\n    },\n    "fr": {\n        "product_not_found": "Produit avec l'ID {product_id} introuvable.",\n        "invalid_input": "Entrée invalide : {error_message}",\n    },\n    "es": {\n        "product_not_found": "Producto con ID {product_id} no encontrado.",\n        "invalid_input": "Entrada inválida: {error_message}",\n    },\n    "de": {\n        "product_not_found": "Produkt mit ID {product_id} nicht gefunden.",\n        "invalid_input": "Ungültige Eingabe: {error_message}",\n    }\n}\n\ndef get_translation(locale: str, key: str, **kwargs) -> str:\n    """Retrieves a translation for a given locale and key.\n    If the locale or key is not found, returns a default message.\n    """\n    if locale in translations and key in translations[locale]:\n        return translations[locale][key].format(**kwargs)\n    return f"Translation missing for key '{key}' in locale '{locale}'."\n\n@app.get("/products/{product_id}")\nasync def get_product(request: Request, product_id: int, locale: str = "en"):\n    # Simulate product lookup\n    if product_id > 100:\n        message = get_translation(locale, "product_not_found", product_id=product_id)\n        raise HTTPException(status_code=404, detail=message)\n\n    if product_id < 0:\n         message = get_translation(locale, "invalid_input", error_message="Product ID must be positive")\n         raise HTTPException(status_code=400, detail=message)\n\n    return {"product_id": product_id, "name": "Example Product"}\n
            

              
                Copy