Path operations (GET, POST, PUT, DELETE) in FastAPI - Performance & Optimization

Performance: Path operations (GET, POST, PUT, DELETE)

MEDIUM IMPACT

This affects server response time and client perceived latency when interacting with API endpoints.

Handling data retrieval and modification via API endpoints

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    # Simulate async processing
    import asyncio
    await asyncio.sleep(0.1)
    return {"item_id": item_id}

@app.post("/items/")
async def create_item(item: dict):
    # Async and validation handled
    return item

Using async functions avoids blocking, allowing concurrent handling of requests and faster responses.

📈 Performance GainReduces blocking time from 2s to 0.1s, improving INP and server throughput.

Handling data retrieval and modification via API endpoints

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/items/{item_id}")
def read_item(item_id: int):
    # Simulate heavy processing
    import time
    time.sleep(2)
    return {"item_id": item_id}

@app.post("/items/")
def create_item(item: dict):
    # No validation or async handling
    return item

Blocking synchronous code with delays and no async support causes slow responses and poor user experience.

📉 Performance CostBlocks event loop for 2 seconds per request, increasing INP and server load.

Performance Comparison

Pattern	Server Blocking	Concurrent Requests	Response Time	Verdict
Synchronous blocking code	High (blocks event loop)	Low (serial processing)	Slow (seconds delay)	[X] Bad
Asynchronous non-blocking code	Low (event loop free)	High (parallel processing)	Fast (milliseconds delay)	[OK] Good

Rendering Pipeline

Path operations define how the server processes HTTP requests and sends responses, impacting the time before the client can render or interact with content.

→Server Processing

→Network Transfer

→Client Rendering

⚠️ BottleneckServer Processing when synchronous/blocking code is used

Core Web Vital Affected

INP

This affects server response time and client perceived latency when interacting with API endpoints.

Optimization Tips

1Use async def for path operations to avoid blocking the server event loop.

2Avoid synchronous blocking calls like time.sleep() in API endpoints.

3Keep path operation logic lightweight to reduce server processing time.

Performance Quiz - 3 Questions

Which path operation style improves server responsiveness in FastAPI?

A Using time.sleep() in synchronous functions

B Blocking database calls without async support

C Using async def with await for I/O operations

D Heavy CPU-bound tasks in synchronous functions

DevTools: Network

How to check: Open DevTools, go to Network tab, make API requests and observe the timing waterfall for each request.

What to look for: Look for long waiting times or blocking in the request timeline indicating slow server response.

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