Utkarsh Rastogi

Posted on Jun 3 • Edited on Jun 20

Day 1: What is FastAPI & Why Developers Love It

#fastapi #python #restapi #pythonframework

Welcome to Day 1 of the FastAPI Bootcamp – A Day-by-Day Guide series!

Over the next few days, we’ll dive into FastAPI — one of the most exciting frameworks in the Python ecosystem for building high-performance APIs.

🧠 What is FastAPI?

FastAPI is a modern, fast (high-performance) web framework for building APIs with Python 3.8+ using standard type hints. It’s designed to make it easy to build APIs quickly and efficiently while writing clean, production-ready code.

Built on top of Starlette for web handling and Pydantic for data validation, FastAPI combines speed, simplicity, and powerful features out of the box.

🔥 Top Features of FastAPI

⚡ High Performance: Built on ASGI, FastAPI is one of the fastest Python web frameworks.
🧾 Automatic Documentation: Generates Swagger UI and ReDoc from your code, instantly.
✅ Data Validation: Uses Pydantic to validate and serialize input/output data automatically.
🧠 Type Hints Support: Enables better editor support, autocompletion, and fewer bugs.
🔄 Async-Ready: First-class support for asynchronous endpoints using async/await.
📦 Modular & Scalable: Easy to structure large applications using routers and dependencies.

🤔 Why FastAPI Over Flask or Django?

Here's a quick comparison of FastAPI with other popular Python web frameworks:

Feature	FastAPI	Flask	Django
Performance	🚀 Very High (ASGI + async support)	⚡ Moderate (WSGI, no native async)	⚡ Moderate (WSGI, limited async support)
API Documentation	✅ Built-in (Swagger, ReDoc)	❌ Requires extensions	❌ Requires third-party packages
Type Hinting & Editor Support	✅ First-class support	❌ Minimal	❌ Limited
Input Validation	✅ Automatic via Pydantic	❌ Manual or via extensions	❌ Form-based, not API-focused
Learning Curve	🟢 Moderate (if familiar with typing)	🟢 Beginner-friendly	🔴 Steeper due to full-stack features
Use Case Focus	🔥 API-first design	🔥 Lightweight web services	🏗️ Full-stack web applications
Async Support	✅ Native (ASGI & async/await)	❌ Experimental	⚠️ Partial, improving over time

🌍 Real-World Use Cases

FastAPI is widely used for:

Building RESTful APIs
Backend services for web/mobile apps
Deploying machine learning models
Microservices in modern architectures
Real-time or async-heavy systems

Big names like Netflix, Uber, and Microsoft are already using FastAPI in production environments.

🧰 Prerequisites for FastAPI on Windows

Before starting, ensure you have:

🐍 Python 3.8+ (I’m using Python 3.12 for this FastAPI series.)
💻 VS Code or any modern code editor
📦 pip (Python package manager)

✅ Check Python Version

Open your terminal (Command Prompt or PowerShell) and run:

python --version

You should see an output like:

If not installed, download it from the official site: https://www.python.org/downloads/

⚙️ FastAPI Setup on Windows

📁 Step 1: Create a Project Folder

mkdir fastapi-demo cd fastapi-demo

🧪 Step 2: Create a Virtual Environment

python -m venv venv

venv\Scripts\activate

⚠️ Note: If you get any error while running this command, try using the below command first then use above command again:

Set-ExecutionPolicy -ExecutionPolicy Unrestricted -Scope CurrentUser

Once activated, your terminal prompt should show (venv) indicating the virtual environment is active.

📦 Step 3: Install FastAPI and Uvicorn

pip install fastapi uvicorn

🧪 Create Your First FastAPI App

Create a file named main.py and add the following code:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello from FastAPI!"}

Run the app using Uvicorn:

uvicorn main:app --reload

Explanation:

main: the name of your Python file (without .py)
app: the FastAPI instance inside your file
--reload: enables auto-reload on code changes (great for development)

Open your browser and visit:

http://127.0.0.1:8000 → See your API response

http://127.0.0.1:8000/docs → Explore auto-generated Swagger docs

🌍 Real-World Use Cases

FastAPI is ideal for:

RESTful APIs & backend services
Machine Learning model serving
Microservices & async-heavy systems
Startups to enterprise-scale applications

🏢 Companies like Netflix, Uber, and Microsoft use it in production!

⚙️ What is Uvicorn?

Uvicorn is a lightning-fast ASGI server used to run FastAPI apps. It supports asynchronous programming, making your APIs scalable and high-performing.

🔹 Built on uvloop and httptools
🔹 Enables async/await support
🔹 Supports hot-reloading during development
🔹 Perfect match for FastAPI's async nature

With FastAPI + Uvicorn, you get near Node.js-level performance — using Python!

✅ Summary

Today you learned:

What FastAPI is and why it's gaining popularity
Key features that make FastAPI stand out from Flask/Django
Real-world use cases and industry adoption
How to set up FastAPI on Windows
Your first “Hello Message” API in FastAPI

This is just the beginning — more exciting stuff coming up in the next few days!

🙏 Credits

Huge thanks to the FastAPI Official Documentation by Sebastián Ramírez (@tiangolo) — the best place to learn and explore everything about FastAPI.

👨‍💻 About Me

Hey there! I’m Utkarsh Rastogi, an AWS Community Builder and passionate cloud-native enthusiast who loves building scalable backend systems and sharing knowledge with the community.

🔗 Connect with me: Utkarsh Rastogi

💬 Share Your Thoughts – I'd Love Your Feedback!

If you enjoyed today's post or learned something new, I'd truly appreciate it if you leave a comment or share your thoughts 👇

Your feedback, questions, or even a quick “🔥 Loved this!” keeps me motivated to continue this journey and share more in the upcoming #FastAPIDaily posts.

✅ What did you find most helpful?

✅ Anything you'd like explained in the next part?

✅ Suggestions for improvement? I’m all ears! 🙌

Let’s grow and learn together — one FastAPI day at a time 🚀