🧩 1. Introduction to FastAPI¶

🚀 What is FastAPI and Why Use It?¶

FastAPI is a modern, high-performance web framework for building APIs with Python 3.7+ based on standard Python type hints.

🔥 Key Benefits:¶

• Speed: FastAPI is one of the fastest Python frameworks, rivaling Node.js and Go.
• Type Safety: Uses Python type hints for automatic request validation and documentation.
• Automatic Docs: Generates interactive Swagger and ReDoc documentation out of the box.
• Async-Ready: Built on Starlette and Pydantic, it supports asynchronous programming natively.
• Developer Experience: Minimal boilerplate, great editor support, and fast iteration.

🧠 Use Cases:¶

• RESTful APIs
• Microservices
• Backend for web/mobile apps
• ML model serving
• Real-time apps (via WebSockets)

🛠️ Installing FastAPI and Uvicorn¶

FastAPI is just the framework. To run it as a web server, you’ll need Uvicorn, an ASGI server.

✅ Step-by-Step Installation¶

1. Create a virtual environment (recommended):

   python -m venv fastapi-env
   source fastapi-env/bin/activate  # On Windows: fastapi-env\Scripts\activate
   

2. Install FastAPI and Uvicorn:

   pip install fastapi uvicorn
   

3. Verify installation:

   python -m pip show fastapi
   python -m pip show uvicorn
   

You’re now ready to build your first API.

👋 First “Hello World” Endpoint¶

Let’s write a minimal FastAPI app that returns a greeting.

📄 Create a file called main.py:¶

from fastapi import FastAPI

app = FastAPI()

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

🧪 Run the server:¶

uvicorn main:app --reload

• main: the filename (without .py)
• app: the FastAPI instance
• -reload: enables hot-reloading during development

🌐 Visit in your browser:¶

• http://127.0.0.1:8000/ → returns JSON: {"message": "Hello, FastAPI!"}
• http://127.0.0.1:8000/docs → Swagger UI (interactive API docs)
• http://127.0.0.1:8000/redoc → ReDoc UI (alternative docs)

🧪 Try It Yourself¶

Change the message or add another route:

@app.get("/greet/{name}")
def greet_user(name: str):
    return {"message": f"Hello, {name}!"}

Visit http://127.0.0.1:8000/greet/your_name and see the personalized response.