Path operations (GET, POST, PUT, DELETE) in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a GET path operation in FastAPI?

A GET path operation is used to retrieve data from the server. It responds to client requests by sending back information without changing anything on the server.

beginner

How does a POST path operation differ from GET in FastAPI?

POST is used to send data to the server to create a new resource. Unlike GET, POST changes the server state by adding new information.

intermediate

What is the purpose of a PUT path operation in FastAPI?

PUT is used to update an existing resource completely. It replaces the current data with the new data sent by the client.

beginner

Explain the DELETE path operation in FastAPI.

DELETE removes a resource from the server. When a client sends a DELETE request, the server deletes the specified data.

intermediate

Show a simple FastAPI example of a GET and POST path operation.

Example:
from fastapi import FastAPI
app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id}

@app.post("/items/")
async def create_item(name: str):
    return {"name": name}

This shows GET to read and POST to create items.

Which HTTP method is used to retrieve data without changing the server state?

A GET

B POST

C PUT

D DELETE

GET requests fetch data and do not modify the server.

Which path operation method in FastAPI is typically used to create a new resource?

A GET

B POST

C PUT

D DELETE

POST sends data to create new resources on the server.

What does the PUT method do in FastAPI?

A Updates or replaces a resource

B Retrieves data

C Deletes a resource

D Creates a new resource

PUT replaces an existing resource with new data.

Which HTTP method should you use to remove a resource in FastAPI?

A POST

B PUT

C DELETE

D GET

DELETE removes the specified resource from the server.

In FastAPI, how do you define a GET path operation for the URL '/users/{user_id}'?

A @app.delete('/users/{user_id}')

B @app.post('/users/{user_id}')

C @app.put('/users/{user_id}')

D @app.get('/users/{user_id}')

GET method is defined with @app.get decorator.

Describe the four main HTTP methods used in FastAPI path operations and their typical uses.

Think about what each method does to the server data.

Write a simple FastAPI example showing how to create GET and DELETE path operations for a resource called 'item'.

Remember to define async functions with proper decorators.

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