Building REST APIs with Flask and FastAPI

📦 What is a REST API?

REST APIs allow applications to communicate over HTTP. In Python, we can use frameworks like Flask and FastAPI to build them efficiently.

🔧 Flask Example

from flask import Flask, jsonify

app = Flask(__name__)

@app.route("/api/greet")
def greet():
    return jsonify({"message": "Hello from Flask!"})

if __name__ == "__main__":
    app.run(debug=True)

Flask allows routing using @app.route. The route /api/greet returns a JSON response when visited. This is how you define API endpoints in Flask.

⚡ FastAPI Example

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Message(BaseModel):
    message: str

@app.get("/api/greet", response_model=Message)
def greet():
    return {"message": "Hello from FastAPI!"}

FastAPI automatically validates and documents your APIs using Pydantic models. The response_model ensures type-checked output. It also provides a Swagger UI by default.

🔍 Comparison Table

• 🚀 FastAPI is faster and has built-in validation/docs
• 🧱 Flask is simpler and more widely used in small apps
• 📜 Both can return JSON and handle RESTful routes easily

✅ Summary

• Flask: Simple and flexible
• FastAPI: Modern, fast, with auto-validation
• Both are great for building APIs in Python