tiangolo/fastapi · error · HTTPException

Item not found

Error message

Item not found

What it means

Same as error 1 in the legacy-style file: GET /items/{item_id} returns 404 when item_id is not a key in fake_db ('foo' or 'bar'). The store is in-memory and resets on restart.

Solutions

  1. GET /items/foo or /items/bar.
  2. Create then read within the same process.
  3. Back fake_db with persistent storage.

Example fix

// before
GET /items/missing
// after
GET /items/foo
Defensive patterns

Strategy: try-catch

Validate before calling

import httpx
KNOWN = {'foo', 'bar'}
item_id = 'foo'
if item_id in KNOWN:
    resp = httpx.get(f'http://localhost:8000/items/{item_id}', headers={'X-Token': 'coneofsilence'})

Type guard

def is_known_item(item_id: object) -> bool:
    return isinstance(item_id, str) and item_id in {'foo', 'bar'}

Try / catch

try:
    resp = httpx.get(url, headers=headers)
    resp.raise_for_status()
except httpx.HTTPStatusError as e:
    if e.response.status_code == 404:
        ...

Prevention

When it happens

Trigger: GET /items/<anything-but-foo-or-bar> with a valid token, or GETting an item created in a previous server process.

Common situations: Post-restart 404s, typos in item_id, or assuming seeded data includes more than foo/bar.

Related errors

AI-assisted analysis of tiangolo/fastapi@3e8d1526d8 (2026-08-11). Data as JSON: /api/errors/2615281d899bd889. Report an issue: GitHub.

Appendix: source

Thrown at docs_src/app_testing/app_b_py310/main.py:25

    "foo": {"id": "foo", "title": "Foo", "description": "There goes my hero"},
    "bar": {"id": "bar", "title": "Bar", "description": "The bartenders"},
}

app = FastAPI()


class Item(BaseModel):
    id: str
    title: str
    description: str | None = None


@app.get("/items/{item_id}", response_model=Item)
async def read_main(item_id: str, x_token: str = Header()):
    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item_id not in fake_db:
        raise HTTPException(status_code=404, detail="Item not found")
    return fake_db[item_id]


@app.post("/items/")
async def create_item(item: Item, x_token: str = Header()) -> Item:
    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item.model_dump()
    return item

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