docs: improve tutorial002.py with clearer comments and docstrings, improve tutorial004.py withdocstrings for the route and exception handler

docs_src/handling_errors/tutorial002.py

@@ -7,6 +7,7 @@ items = {"foo": "The Foo Wrestlers"}
 
 @app.get("/items-header/{item_id}")
 async def read_item_header(item_id: str):
+    
     if item_id not in items:
         raise HTTPException(
             status_code=404,

docs_src/handling_errors/tutorial004.py

@@ -1,23 +1,42 @@
-from fastapi import FastAPI, HTTPException
+from fastapi import FastAPI, HTTPException, Request
 from fastapi.exceptions import RequestValidationError
-from fastapi.responses import PlainTextResponse
+from fastapi.responses import JSONResponse
 from starlette.exceptions import HTTPException as StarletteHTTPException
+from fastapi.encoders import jsonable_encoder
+from starlette import status
 
 app = FastAPI()
 
 
 @app.exception_handler(StarletteHTTPException)
-async def http_exception_handler(request, exc):
-    return PlainTextResponse(str(exc.detail), status_code=exc.status_code)
-
+async def http_exception_handler(request: Request, exc: StarletteHTTPException):
+    """
+    Handles all HTTPException (Starlette) errors.
+    Returns a JSON response with status code and detail.
+    """
+    return JSONResponse(
+        status_code=exc.status_code,
+        content={"message": exc.detail}
+    )
 
 @app.exception_handler(RequestValidationError)
-async def validation_exception_handler(request, exc):
-    return PlainTextResponse(str(exc), status_code=400)
+async def validation_exception_handler(request: Request, exc: RequestValidationError):
+    """
+    Handles validation errors for request data.
+    Returns a JSON response with 400 status and error details.
+    """
+    return JSONResponse(
+        status_code=status.HTTP_400_BAD_REQUEST,
+        content=jsonable_encoder({"errors": exc.errors(), "body": exc.body})
+    )
 
 
 @app.get("/items/{item_id}")
 async def read_item(item_id: int):
+    
     if item_id == 3:
-        raise HTTPException(status_code=418, detail="Nope! I don't like 3.")
+        raise HTTPException(
+            status_code=418,
+            detail="Nope! I don't like 3."
+        )
     return {"item_id": item_id}