Streaming responses in FastAPI - Mini Project: Build & Apply

Streaming Responses with FastAPI

📖 Scenario: You are building a simple web API that sends data to users in small parts instead of all at once. This is useful when sending large files or live updates.

🎯 Goal: Create a FastAPI app that streams a sequence of messages to the client one by one.

📋 What You'll Learn

Create a FastAPI app instance

Define a generator function that yields messages

Create a GET endpoint that returns a streaming response using the generator

Set the correct media type for streaming text data

💡 Why This Matters

🌍 Real World

Streaming responses are used in real-time data feeds, large file downloads, or live event updates where sending data in chunks improves performance and user experience.

💼 Career

Understanding streaming responses is important for backend developers building efficient APIs that handle large or continuous data without blocking the server or client.

1

Create the FastAPI app

Write code to create a FastAPI app instance called app.

FastAPI

# Create the FastAPI app instance
# Your code here

Need a hint?

Use FastAPI() to create the app instance and assign it to app.

2

Define a generator function to yield messages

Define a function called message_stream that yields three strings: 'Hello', 'from', and 'FastAPI' one by one.

FastAPI

from fastapi import FastAPI

app = FastAPI()

# Define the generator function
# Your code here

Need a hint?

Use yield to send each message one at a time inside the function.

3

Create a GET endpoint that streams the messages

Add a GET endpoint at path /stream using @app.get("/stream"). The endpoint function called stream_messages should return a StreamingResponse that streams data from message_stream.

FastAPI

from fastapi import FastAPI
from fastapi.responses import StreamingResponse

app = FastAPI()

def message_stream():
    yield "Hello"
    yield "from"
    yield "FastAPI"

# Create the GET endpoint to stream messages
# Your code here

Need a hint?

Use StreamingResponse from fastapi.responses and set media_type to "text/plain".

4

Complete the streaming response setup

Ensure the StreamingResponse correctly streams the generator output with the media type text/plain in the stream_messages function.

FastAPI

from fastapi import FastAPI
from fastapi.responses import StreamingResponse

app = FastAPI()

def message_stream():
    yield "Hello"
    yield "from"
    yield "FastAPI"

@app.get("/stream")
def stream_messages():
    # Return the streaming response with correct media type
    # Your code here

Need a hint?

Make sure the StreamingResponse uses message_stream() and media_type="text/plain".