Features

 Link : https://www.youtube.com/watch?v=H9Blu0kWdZE&list=PLK8U0kF0E_D6l19LhOGWhVZ3sQ6ujJKq_


1. Automatic docs :  

Fast API provides a swagger UI which shows what are the routes we have created and what are the 

-- Swagger UI
-- ReDoc

 Fast API : https://fastapi.tiangolo.com/

  

Core FastAPI Terminologies

 1. App Instance

from fastapi import FastAPI
app = FastAPI()

 

This is your main application object.

Everything (routes, configs) is attached to this.

 

2. Path Operation (Route)

@app.get("/users")

A path = URL (/users)

An operation = HTTP method (GET, POST, etc.)

Together: Path Operation

👉 Meaning:

“When a GET request comes to /users, run this function.”

 

3. HTTP Methods

• GET → Read data
• POST → Create data
• PUT → Update (full)
• PATCH → Update (partial)
• DELETE → Remove

 4. Path Parameters

@app.get("/users/{user_id}")
def get_user(user_id: int):

 

Dynamic values in the URL

Example: /users/10 → user_id = 10

 5. Query Parameters

 @app.get("/users")
def get_users(limit: int = 10):

Comes after ? in URL

Example: /users?limit=5

 

 6. Request Body

from pydantic import BaseModel

class User(BaseModel):
    name: str
    age: int

@app.post("/users")
def create_user(user: User): 

Data sent in request (usually JSON)

Validated using Pydantic

 

7. Pydantic Models

• Used for:
  • Validation
  • Serialization
• Ensures correct data types\

 

8. Response Model

  @app.get("/users", response_model=User)

 

Defines what the API returns

Filters and validates output

 

9. Dependency Injection

from fastapi import Depends

def get_db():
    return "DB Connection"

@app.get("/")
def read(db = Depends(get_db)):

 

Reusable logic (DB, auth, etc.)

Injected automatically

  

10. Middleware

• Runs before/after every request
• Used for:
  • Logging
  • Authentication
  • CORS

 

11. Status Codes

from fastapi import status

@app.get("/", status_code=status.HTTP_200_OK) 

12. Exception Handling

from fastapi import HTTPException

raise HTTPException(status_code=404, detail="Not found")

 

13. APIRouter

from fastapi import APIRouter
router = APIRouter()

 Used to split large apps into modules

 

14. OpenAPI & Docs

• Auto-generated docs:
  • /docs → Swagger UI
  • /redoc → ReDoc

 15. Async / Await

@app.get("/")
async def read():

Enables high performance (non-blocking)

 

🧠 Simple Mental Model

Think of FastAPI like this:

URL → Route → Function → Validate Input → Process → Return Response