Module 29 - FastAPI Introduction

FastAPI is a modern, fast web framework for building APIs with Python, featuring automatic interactive documentation and data validation.

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1. Introduction

Installation

pip install fastapi uvicorn

Why FastAPI?

✅ Fast performance (comparable to NodeJS/Go)
✅ Automatic API documentation
✅ Type hints and validation
✅ Async support built-in
✅ Easy to learn

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2. Hello World

from fastapi import FastAPI

app = FastAPI()

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

# Run with: uvicorn main:app --reload

Visit:

• API: http://127.0.0.1:8000/
• Docs: http://127.0.0.1:8000/docs

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3. Path and Query Parameters

from fastapi import FastAPI

app = FastAPI()

# Path parameter
@app.get("/users/{user_id}")
def read_user(user_id: int):
    return {"user_id": user_id}

# Query parameters
@app.get("/items/")
def read_items(skip: int = 0, limit: int = 10):
    return {"skip": skip, "limit": limit}

# Combined
@app.get("/users/{user_id}/items/")
def read_user_items(user_id: int, skip: int = 0):
    return {"user_id": user_id, "skip": skip}

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4. Pydantic Models

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float
    is_offer: bool = False

@app.post("/items/")
def create_item(item: Item):
    return {"item": item, "message": "Item created"}

@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    return {"item_id": item_id, "item": item}

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5. CRUD Operations

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from typing import List

app = FastAPI()

class User(BaseModel):
    id: int
    name: str
    email: str

users_db = []

@app.post("/users/", response_model=User)
def create_user(user: User):
    users_db.append(user)
    return user

@app.get("/users/", response_model=List[User])
def get_users():
    return users_db

@app.get("/users/{user_id}", response_model=User)
def get_user(user_id: int):
    for user in users_db:
        if user.id == user_id:
            return user
    raise HTTPException(status_code=404, detail="User not found")

@app.delete("/users/{user_id}")
def delete_user(user_id: int):
    for i, user in enumerate(users_db):
        if user.id == user_id:
            users_db.pop(i)
            return {"message": "User deleted"}
    raise HTTPException(status_code=404, detail="User not found")

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Summary

✅ FastAPI is modern and fast
✅ Automatic documentation with Swagger UI
✅ Pydantic models for validation
✅ Type hints throughout
✅ Async support built-in

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Next Steps

In Module 30, you'll learn:

• Testing with pytest
• Unit tests and fixtures
• Test coverage
• Mocking and assertions

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Practice Exercises

1. Create a complete REST API for a todo app
2. Build an API with authentication
3. Implement pagination for list endpoints
4. Create a blog API with posts and comments
5. Build a file upload API :::