Sending and receiving messages in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import FastAPI and create an app instance.

FastAPI

from fastapi import [1]

app = [1]()

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

AResponse

BRequest

CFastAPI

DDepends

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request or Response instead of FastAPI

Not creating an instance of FastAPI

You need to import FastAPI and create an instance of it to start your app.

2fill in blank

medium

Complete the code to define a GET endpoint that returns a welcome message.

FastAPI

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

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

Apost

Bget

Cput

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.post instead of @app.get

Forgetting the decorator

The @app.get decorator defines a GET HTTP method endpoint.

3fill in blank

hard

Fix the error in the code to receive JSON data in a POST request.

FastAPI

from fastapi import FastAPI, [1]

app = FastAPI()

@app.post("/items")
async def create_item(item = [1]()):
    return item

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

ABody

BQuery

CPath

DHeader

Attempts:

3 left

💡 Hint

Common Mistakes

Using Query or Path instead of Body

Not importing Body

Use Body to declare that the parameter should come from the request body as JSON.

4fill in blank

hard

Fill both blanks to define a POST endpoint that receives a message and returns it with a status.

FastAPI

from fastapi import FastAPI, [1]
from pydantic import BaseModel

app = FastAPI()

class Message(BaseModel):
    text: str

@app.post("/send")
async def send_message(message: [2] = [1]()):
    return {"status": "received", "message": message.text}

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

ABody

BQuery

CMessage

DPath

Attempts:

3 left

💡 Hint

Common Mistakes

Using Query or Path instead of Body

Using wrong type annotation for message

Use Body to receive the message from the request body and Message as the data model.

5fill in blank

hard

Fill all three blanks to create a WebSocket endpoint that sends back received messages.

FastAPI

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/[1]")
async def websocket_endpoint(websocket: [2]):
    await websocket.accept()
    data = await websocket.[3]()
    await websocket.send_text(f"Message received: {data}")

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

Aws

BWebSocket

Creceive_text

Dhttp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'http' instead of 'ws' in the path

Wrong parameter type instead of WebSocket

Using receive() instead of receive_text()

The WebSocket endpoint path is usually something like '/ws'. The parameter type is WebSocket. To receive text data, use receive_text().

Practice

1. What is the main purpose of using Pydantic models in FastAPI when sending and receiving messages?

easy

A. To create HTML templates for message display

B. To manage user authentication tokens

C. To handle database connections automatically

D. To clearly define the structure and data types of messages

Solution

1. Step 1: Understand Pydantic's role in FastAPI

   Pydantic models define how data should look, including types and required fields.

2. Step 2: Connect Pydantic to message handling

   Using Pydantic ensures messages sent or received follow a clear, expected format.

3. Final Answer:

   To clearly define the structure and data types of messages -> Option D

4. Quick Check:

   Pydantic models = message structure [OK]

Hint: Pydantic models describe message shape and types [OK]

Common Mistakes:

• Confusing Pydantic with HTML templating
• Thinking Pydantic manages databases
• Assuming Pydantic handles authentication

2. Which of the following is the correct way to declare a POST endpoint in FastAPI that receives a message model named Message?

easy

A. @app.post('/send')\ndef send_message():\n return Message

B. @app.post('/send')\nasync def send_message(msg: Message):\n return msg

C. @app.get('/send')\nasync def send_message(msg: Message):\n return msg

D. @app.put('/send')\nasync def send_message(msg: Message):\n return msg

Solution

1. Step 1: Identify the HTTP method for sending messages

   POST is used to send data to the server, so @app.post is correct.

2. Step 2: Check function signature for receiving a Pydantic model

   Function must accept a parameter typed as Message to receive the message body.

3. Final Answer:

   @app.post('/send')\nasync def send_message(msg: Message):\n return msg -> Option B

4. Quick Check:

   POST + typed param = correct endpoint [OK]

Hint: Use @app.post and typed parameter for message body [OK]

Common Mistakes:

• Using GET instead of POST for sending data
• Missing parameter type annotation
• Using wrong HTTP method like PUT

3. Given this FastAPI endpoint code, what will be the response when sending a POST request with JSON {"text": "Hello"}?

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Message(BaseModel):
    text: str

@app.post('/echo')
async def echo_message(msg: Message):
    return {"message": msg.text.upper()}

medium

A. {"message": "HELLO"}

B. {"message": "Hello"}

C. {"text": "HELLO"}

D. 500 Internal Server Error

Solution

1. Step 1: Understand the input and model

   The input JSON has key "text" with value "Hello", matching Message model.

2. Step 2: Analyze the endpoint return

   The function returns a dict with key "message" and value as msg.text.upper(), which converts "Hello" to "HELLO".

3. Final Answer:

   {"message": "HELLO"} -> Option A

4. Quick Check:

   Uppercase text returned in 'message' key [OK]

Hint: Look for .upper() call on input text [OK]

Common Mistakes:

• Returning original text without uppercasing
• Returning wrong key name in response
• Expecting an error instead of valid response

4. What is wrong with this FastAPI endpoint code for receiving a message?

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Message(BaseModel):
    content: str

@app.post('/receive')
def receive_message(msg: Message):
    return {"received": msg.content}

medium

A. The endpoint function is missing async keyword

B. The parameter msg should be annotated with Request

C. The endpoint must use @app.get instead of @app.post

D. The function must return a Pydantic model instance

Solution

1. Step 1: Check function declaration for FastAPI async support

   FastAPI supports async endpoints; missing async can cause blocking or warnings.

2. Step 2: Verify parameter and decorator correctness

   Parameter is correctly typed as Message; @app.post is correct for receiving data.

3. Final Answer:

   The endpoint function is missing async keyword -> Option A

4. Quick Check:

   Async keyword needed for async endpoints [OK]

Hint: Use async def for FastAPI POST endpoints [OK]

Common Mistakes:

• Using sync def without async in async context
• Wrong HTTP method decorator
• Incorrect parameter type annotation

5. You want to create a FastAPI endpoint that receives a list of messages, each with a text field, and returns a list of all texts in uppercase. Which code snippet correctly implements this?

hard

A. from fastapi import FastAPI
from pydantic import BaseModel
from typing import List

app = FastAPI()

class Message(BaseModel):
text: str

@app.get('/batch')
def batch_messages(msgs: List[Message]):
return [msg.text.upper() for msg in msgs]

B. from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Message(BaseModel):
text: str

@app.post('/batch')
async def batch_messages(msgs: Message):
return [msg.text.upper() for msg in msgs]

C. from fastapi import FastAPI
from pydantic import BaseModel
from typing import List

app = FastAPI()

class Message(BaseModel):
text: str

@app.post('/batch')
async def batch_messages(msgs: List[Message]):
return [msg.text.upper() for msg in msgs]

D. from fastapi import FastAPI
from pydantic import BaseModel
from typing import List

app = FastAPI()

class Message(BaseModel):
text: str

@app.post('/batch')
async def batch_messages(msgs: List[str]):
return [text.upper() for text in msgs]

Solution

1. Step 1: Use List[Message] to receive multiple messages

   Typing msgs as List[Message] allows FastAPI to parse a list of message objects.

2. Step 2: Return uppercase texts from each message

   List comprehension extracts each msg.text and converts it to uppercase correctly.

3. Final Answer:

   Code snippet with List[Message] parameter and async POST endpoint -> Option C

4. Quick Check:

   List of Message + async POST + uppercase list [OK]

Hint: Use List[Message] and async POST for batch message input [OK]

Common Mistakes:

• Using single Message instead of list
• Using GET instead of POST for sending data
• Typing list as List[str] instead of List[Message]