Trailing slash behavior in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the response status when accessing a FastAPI route without trailing slash if the route is defined with trailing slash?

Consider this FastAPI route:

from fastapi import FastAPI
app = FastAPI()

@app.get("/items/")
async def read_items():
    return {"message": "Hello"}

What happens when you request /items (without trailing slash)?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/items/")
async def read_items():
    return {"message": "Hello"}

A FastAPI responds with a 307 redirect to /items/ (adds trailing slash)

B FastAPI responds with 200 OK and returns the JSON directly

C FastAPI returns 404 Not Found error

D FastAPI responds with 500 Internal Server Error

💡 Hint

Think about how FastAPI handles routes with trailing slashes and requests without them.

FastAPI automatically redirects requests missing a trailing slash to the route with trailing slash using a 307 Temporary Redirect status.

❓ component_behavior

intermediate

What happens when you define a FastAPI route without trailing slash and request it with trailing slash?

Given this route:

from fastapi import FastAPI
app = FastAPI()

@app.get("/users")
async def read_users():
    return {"users": []}

What is the response when requesting /users/ (with trailing slash)?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/users")
async def read_users():
    return {"users": []}

A FastAPI responds with 500 Internal Server Error

B FastAPI responds with 307 redirect to /users (removes trailing slash)

C FastAPI responds with 404 Not Found error

D FastAPI responds with 200 OK and returns the JSON

💡 Hint

Check how FastAPI treats trailing slashes when the route is defined without one.

FastAPI does not redirect from a URL with trailing slash to one without. It treats them as different routes, so /users/ returns 404 if only /users is defined.

📝 Syntax

advanced

Which route definition causes a syntax error in FastAPI?

Select the option that will cause a syntax error when defining a FastAPI route related to trailing slashes.

A

@app.get("/path")
async def func():
    return {}

B

@app.get("/path//")
async def func():
    return {}

C

@app.get("/path/{id}/")
async def func(id: int):
    return {"id": id}

D

@app.get("/path/")
async def func():
    return {}

💡 Hint

Check the route string for invalid characters or patterns.

Double slashes in route paths like "/path//" are invalid and cause a syntax error in FastAPI route definitions.

❓ state_output

advanced

What is the final URL path after FastAPI redirects when requesting a route without trailing slash if route has trailing slash?

Given this route:

@app.get("/products/")
async def get_products():
    return {"products": []}

If you request /products, what URL will the browser end up at after FastAPI's redirect?

A /products/

B /products//

C /products

D /products/index

💡 Hint

FastAPI adds or removes trailing slashes to match route definitions.

FastAPI redirects to the route with trailing slash if the route is defined with trailing slash, so the final URL is /products/.

🔧 Debug

expert

Why does this FastAPI app return 404 when requesting /api/items/ even though route is defined as /api/items?

Code snippet:

from fastapi import FastAPI
app = FastAPI()

@app.get("/api/items")
async def items():
    return {"items": [1,2,3]}

Requesting /api/items/ returns 404. Why?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/api/items")
async def items():
    return {"items": [1,2,3]}

A The server is misconfigured and blocks trailing slash URLs

B The route handler has a syntax error causing 404

C FastAPI automatically removes trailing slashes, so /api/items/ is invalid

D FastAPI treats /api/items and /api/items/ as different routes and does not redirect from /api/items/ to /api/items

💡 Hint

Think about how FastAPI handles trailing slashes when the route is defined without one.

FastAPI does not redirect from a URL with trailing slash to one without. They are treated as different routes, so /api/items/ returns 404 if only /api/items is defined.