Trailing slash behavior in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a FastAPI route that responds to GET requests at '/items/'.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/items[1]")
def read_items():
    return {"message": "Items list"}

Drag options to blanks, or click blank then click option'

A/

C//

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the trailing slash when the route expects it causes a 404 error.

Using double slashes '//' is invalid syntax for route paths.

The trailing slash '/' in the route path means the URL must end with a slash to match this route.

2fill in blank

medium

Complete the code to define a FastAPI route that responds to GET requests at '/users' without a trailing slash.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/users[1]")
def read_users():
    return {"message": "Users list"}

Drag options to blanks, or click blank then click option'

A/

C//

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a trailing slash when the route is defined without one causes 404 errors.

Using double slashes '//' is invalid and causes errors.

Omitting the trailing slash means the route matches URLs without a slash at the end.

3fill in blank

hard

Fix the error in the route decorator to correctly handle requests to '/products/'.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/products[1]")
def read_products():
    return {"message": "Products list"}

Drag options to blanks, or click blank then click option'

B/

Cproducts

D//

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving out the trailing slash causes 404 errors when the URL ends with a slash.

Using double slashes '//' is invalid.

The route must include the trailing slash '/' to match URLs ending with '/products/'.

4fill in blank

hard

Complete the code to create a route that matches '/orders' without a trailing slash and returns a JSON message.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/orders")
def read_orders():
    return {"message": "Orders[1]"}

Drag options to blanks, or click blank then click option'

B/

C list

Ds

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a slash in BLANK_1 causes route mismatch.

Not adding descriptive text in the message makes output unclear.

The route path has no trailing slash, so BLANK_1 is empty. The message adds ' list' to 'Orders' for clarity.

5fill in blank

hard

Fill all three blanks to define a route that matches '/customers/' with trailing slash and returns a JSON with key 'name' and value 'Customer'.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/customers[1]")
def read_customers():
    return {{"[2]": "[3]"}}

Drag options to blanks, or click blank then click option'

A/

Bname

CCustomer

Dcustomer

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the trailing slash causes route mismatch.

Using wrong keys or values in the returned JSON.

The route includes a trailing slash '/'. The returned JSON has key 'name' and value 'Customer'.

Practice

1. In FastAPI, what happens if you define a route with a trailing slash like @app.get('/items/') and a client requests /items without the slash?

easy

A. FastAPI will redirect the client to /items/ automatically.

B. FastAPI will return a 404 Not Found error.

C. FastAPI will treat both URLs as the same without any redirect.

D. FastAPI will raise a server error.

Solution

1. Step 1: Understand FastAPI's default trailing slash behavior

   FastAPI automatically redirects requests without a trailing slash to the route with a trailing slash if defined that way.

2. Step 2: Apply this to the given route

   Since the route is defined with a trailing slash, a request to /items will redirect to /items/.

3. Final Answer:

   FastAPI will redirect the client to /items/ automatically. -> Option A

4. Quick Check:

   Trailing slash route causes redirect = C [OK]

Hint: Trailing slash routes redirect missing slash URLs [OK]

Common Mistakes:

• Thinking FastAPI treats slash and no-slash URLs identically without redirect
• Assuming 404 error on missing slash
• Believing server error occurs

2. Which of the following is the correct way to define a FastAPI route that matches exactly /users without a trailing slash?

easy

A. @app.get('/users/')

B. @app.get('/users')

C. @app.get('/users/*')

D. @app.get('/users?')

Solution

1. Step 1: Recall route syntax for exact path matching

   To match a path without trailing slash exactly, define the route without the slash.

2. Step 2: Check each option

   @app.get('/users') uses @app.get('/users') which matches /users exactly without trailing slash.

3. Final Answer:

   @app.get('/users') -> Option B

4. Quick Check:

   Exact no-slash route = D [OK]

Hint: No trailing slash in route means no slash in URL [OK]

Common Mistakes:

• Adding trailing slash when none is wanted
• Using wildcard or query syntax incorrectly
• Confusing optional trailing slash with exact match

3. Given this FastAPI code snippet:

@app.get('/products')
async def get_products():
    return {'message': 'No slash'}

@app.get('/products/')
async def get_products_slash():
    return {'message': 'With slash'}

What will be the JSON response when a client requests /products/?

medium

A. {'message': 'With slash'}

B. {'message': 'No slash'}

C. 404 Not Found error

D. Redirect to /products without slash

Solution

1. Step 1: Identify route matching for /products/

   The route @app.get('/products/') matches the URL /products/ exactly.

2. Step 2: Determine which function runs

   The function get_products_slash handles /products/ and returns {'message': 'With slash'}.

3. Final Answer:

   {'message': 'With slash'} -> Option A

4. Quick Check:

   Trailing slash URL matches trailing slash route = A [OK]

Hint: Trailing slash URL matches trailing slash route exactly [OK]

Common Mistakes:

• Assuming no slash route handles slash URL
• Expecting redirect instead of direct match
• Confusing 404 error with route mismatch

4. You have this FastAPI route:

@app.get('/orders')

But when you request /orders/ with a trailing slash, you get a 404 error. How can you fix this to accept both /orders and /orders/ without errors?

medium

A. Add a middleware to ignore trailing slashes

B. Change the route to @app.get('/orders/') only

C. Use a wildcard route like @app.get('/orders*')

D. Define a second route with trailing slash: @app.get('/orders/')

Solution

1. Step 1: Understand FastAPI's strict matching

   FastAPI treats /orders and /orders/ as different routes and does not match one to the other automatically unless redirect applies.

2. Step 2: Add explicit route for trailing slash

   Defining @app.get('/orders/') alongside @app.get('/orders') allows both URLs to be handled without 404.

3. Final Answer:

   Define a second route with trailing slash: @app.get('/orders/') -> Option D

4. Quick Check:

   Explicit routes for both slash and no-slash = A [OK]

Hint: Add both slash and no-slash routes to avoid 404 [OK]

Common Mistakes:

• Assuming one route handles both URLs automatically
• Using wildcard incorrectly
• Expecting middleware to fix trailing slash issues by default

5. You want a FastAPI route to accept both /profile and /profile/ URLs without redirect or 404 errors, and return the same response. Which approach is best?

hard

A. Define one route with trailing slash and rely on FastAPI redirect.

B. Define one route without trailing slash and rely on FastAPI redirect.

C. Define two routes: @app.get('/profile') and @app.get('/profile/') with the same function.

D. Use a custom middleware to strip trailing slashes before routing.

Solution

1. Step 1: Understand FastAPI's redirect behavior

   FastAPI redirects missing trailing slash URLs to the defined route with trailing slash, but this causes a redirect, not direct handling.

2. Step 2: Avoid redirects by defining both routes

   Defining both @app.get('/profile') and @app.get('/profile/') with the same function handles both URLs directly without redirect or 404.

3. Final Answer:

   Define two routes: @app.get('/profile') and @app.get('/profile/') with the same function. -> Option C

4. Quick Check:

   Two explicit routes avoid redirect and 404 = B [OK]

Hint: Define both slash and no-slash routes for no redirect [OK]

Common Mistakes:

• Relying on redirect when direct handling is needed
• Using middleware unnecessarily
• Defining only one route expecting both URLs to work