Path operations (GET, POST, PUT, DELETE) in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a GET path operation that returns a welcome message.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.[1]("/")
async def read_root():
    return {"message": "Welcome to FastAPI!"}

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

Aget

Bpost

Cput

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST instead of GET for retrieving data.

The @app.get decorator defines a GET path operation, which is used to retrieve data.

2fill in blank

medium

Complete the code to create a POST path operation that accepts an item name and returns it.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str

@app.[1]("/items/")
async def create_item(item: Item):
    return {"item_name": item.name}

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

Apost

Bget

Cput

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET instead of POST when sending data to create.

The @app.post decorator defines a POST path operation, which is used to create new data.

3fill in blank

hard

Fix the error in the code to update an item using PUT method.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str

@app.[1]("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    return {"item_id": item_id, "updated_name": item.name}

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

Apost

Bdelete

Cget

Dput

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST or GET instead of PUT for updates.

The @app.put decorator is used for updating existing data, which fits the update operation.

4fill in blank

hard

Fill both blanks to create a DELETE path operation that deletes an item by its ID.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.[1]("/items/[2]")
async def delete_item(item_id: int):
    return {"message": f"Item {item_id} deleted"}

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

Adelete

Bpost

C{item_id}

D/item_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST or GET instead of DELETE.

Using incorrect path parameter syntax.

The @app.delete decorator defines a DELETE path operation. The path must include {item_id} to capture the item ID from the URL.

5fill in blank

hard

Fill all three blanks to create a PUT path operation that updates an item and returns its ID and new name.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str

@app.[1]("/items/[2]")
async def update_item([3]: int, item: Item):
    return {"item_id": [3], "new_name": item.name}

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

Aput

Bitem_id

C{item_id}

Dpost

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching path parameter names.

Using POST instead of PUT.

The @app.put decorator is for updating. The path parameter and function argument must be named item_id to match the URL.

Practice

1. Which HTTP method in FastAPI is typically used to retrieve data without changing anything on the server?

easy

A. DELETE

B. POST

C. PUT

D. GET

Solution

1. Step 1: Understand HTTP methods purpose

   GET is used to read or retrieve data without modifying it.

2. Step 2: Match method to FastAPI operation

   FastAPI uses @app.get() decorator for GET requests to fetch data.

3. Final Answer:

   GET -> Option D

4. Quick Check:

   GET = Read data [OK]

Hint: GET always fetches data without side effects [OK]

Common Mistakes:

• Confusing GET with POST which creates data
• Using PUT for reading data
• Thinking DELETE retrieves data

2. Which of the following is the correct syntax to define a POST path operation in FastAPI to create a new item?

easy

A. @app.post('/items/')\ndef create_item(): pass

B. @app.get('/items/')\ndef create_item(): pass

C. @app.put('/items/')\ndef create_item(): pass

D. @app.delete('/items/')\ndef create_item(): pass

Solution

1. Step 1: Identify the HTTP method for creating data

   POST is used to create new resources in REST APIs.

2. Step 2: Match FastAPI decorator for POST

   FastAPI uses @app.post() decorator to handle POST requests.

3. Final Answer:

   @app.post('/items/')\ndef create_item(): pass -> Option A

4. Quick Check:

   POST = Create data [OK]

Hint: Use @app.post() for creating new data [OK]

Common Mistakes:

• Using @app.get() for creating data
• Confusing PUT with POST
• Using DELETE for creation

3. What will be the response when this FastAPI code is called with a PUT request to update item with id 5?

from fastapi import FastAPI
app = FastAPI()

items = {5: "old value"}

@app.put('/items/{item_id}')
async def update_item(item_id: int):
    items[item_id] = "new value"
    return items[item_id]

medium

A. "new value"

B. "old value"

C. KeyError

D. None

Solution

1. Step 1: Understand the PUT operation code

   The function updates the dictionary value for the given item_id to "new value".

2. Step 2: Check the returned value

   The function returns the updated value, which is "new value".

3. Final Answer:

   "new value" -> Option A

4. Quick Check:

   PUT updates and returns new value [OK]

Hint: PUT replaces existing data and returns updated value [OK]

Common Mistakes:

• Expecting old value after update
• Thinking KeyError occurs without check
• Assuming None is returned

4. Identify the error in this FastAPI DELETE operation code:

from fastapi import FastAPI
app = FastAPI()

items = {1: "apple", 2: "banana"}

@app.delete('/items/{item_id}')
async def delete_item(item_id: int):
    del items[item_id]
    return {"message": "Item deleted"}

medium

A. Missing return statement

B. Wrong HTTP method decorator

C. Deleting item without checking if it exists

D. Function should not be async

Solution

1. Step 1: Analyze the delete operation

   The code deletes an item by key without verifying if the key exists in the dictionary.

2. Step 2: Understand possible runtime error

   If the item_id does not exist, del will raise a KeyError causing a server error.

3. Final Answer:

   Deleting item without checking if it exists -> Option C

4. Quick Check:

   Delete needs existence check [OK]

Hint: Always check if item exists before deleting [OK]

Common Mistakes:

• Assuming item always exists
• Ignoring KeyError on delete
• Thinking async is wrong here

5. You want to create a FastAPI app that supports all four main HTTP methods (GET, POST, PUT, DELETE) for managing a list of users stored in a dictionary. Which approach correctly handles updating a user only if it exists, creating a new user, retrieving a user by ID, and deleting a user safely?

hard

A. Use @app.get to retrieve, @app.post to create, @app.put to update without checking existence, and @app.delete to delete without checking existence

B. Use @app.get to retrieve, @app.post to create, @app.put to update with existence check, and @app.delete to delete with existence check

C. Use only @app.post for all operations to simplify code

D. Use @app.put to create and update, @app.get to delete, @app.post to retrieve

Solution

1. Step 1: Match HTTP methods to CRUD operations

   GET retrieves, POST creates, PUT updates, DELETE removes resources.

2. Step 2: Ensure safe update and delete

   Update and delete should check if the user exists to avoid errors.

3. Final Answer:

   Use @app.get to retrieve, @app.post to create, @app.put to update with existence check, and @app.delete to delete with existence check -> Option B

4. Quick Check:

   Correct HTTP methods with safety checks [OK]

Hint: Match HTTP verbs to actions and check existence before update/delete [OK]

Common Mistakes:

• Skipping existence checks causing errors
• Using wrong HTTP methods for actions
• Trying to do all actions with one method