April Python Bootcamp Day 16

 

Day 16: Working with APIs using FastAPI

Introduction to APIs

An API (Application Programming Interface) acts as a bridge that allows two software systems to communicate with each other.

Basic Flow:

• Client (You/App) → Sends a request
• Server → Processes the request
• Server → Sends a response

Real-Life Example: Weather App

• App sends a request to a weather API
• API processes it
• API returns weather data (temperature, humidity, etc.)

---

Types of APIs

1. REST API

• Most commonly used
• Uses HTTP methods
• Example: Food delivery apps (Swiggy, Zomato)

2. SOAP API

• More secure, structured
• Used in banking systems
• Example: Bank transactions

3. GraphQL API

• Fetch only required data
• Flexible and efficient
• Example: Modern web apps

---

HTTP Methods (Core of APIs)

Method	Purpose
GET	Fetch data
POST	Send data
PUT	Update data
DELETE	Delete data

---

What is FastAPI?

FastAPI is a modern Python web framework used to build APIs quickly and efficiently.

Key Features:

• High performance (uses async)
• Automatic API documentation (Swagger UI)
• Easy to learn
• Built-in validation using Pydantic

---

What is JSON?

JSON (JavaScript Object Notation) is the standard format used to exchange data between client and server.

Example:

{
  "name": "Piyush",
  "age": 21
}

---

What is Pydantic?

Pydantic ensures:

• Data validation
• Correct structure
• Type safety

---

Basic FastAPI Example

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

@app.get("/")
def home():
    return {"message": "Welcome to FastAPI!"}

@app.get("/users")
def get_users():
    return ["Piyush", "Aman", "Amit"]

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

@app.post("/create-user")
def create_user(user: dict):
    return {
        "message": "User created successfully",
        "user": user
    }

---

Using Pydantic Model

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

@app.post("/user-create")
def create_user1(user: User):
    return {
        "name": user.name,
        "age": user.age
    }

---

CRUD API Example (Students)

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel

app = FastAPI()

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

students = {}

@app.get("/students")
def get_students():
    return students

@app.get("/students/{student_id}")
def get_student(student_id: int):
    if student_id not in students:
        raise HTTPException(status_code=404, detail="Student not found")
    return students[student_id]

@app.post("/students/{student_id}")
def create_student(student_id: int, student: Student):
    if student_id in students:
        raise HTTPException(status_code=400, detail="Student already exists")
    students[student_id] = student
    return {"message": "Student created", "data": student}

@app.put("/students/{student_id}")
def update_student(student_id: int, student: Student):
    if student_id not in students:
        raise HTTPException(status_code=404, detail="Student not found")
    students[student_id] = student
    return {"message": "Student updated", "data": student}

@app.delete("/students/{student_id}")
def delete_student(student_id: int):
    if student_id not in students:
        raise HTTPException(status_code=404, detail="Student not found")
    del students[student_id]
    return {"message": "Student deleted"}

---

Summary

• APIs enable communication between systems
• HTTP methods define operations
• FastAPI simplifies API development
• JSON is used for data exchange
• Pydantic ensures data validation
• CRUD operations are essential for real-world APIs

---

Assignment Questions

Theory-Based

1. What is an API? Explain with a real-world example.
2. Differentiate between REST, SOAP, and GraphQL APIs.
3. What are HTTP methods? Explain each with use cases.
4. Why is JSON used in APIs?
5. What is the role of Pydantic in FastAPI?

---

Practical Questions

1. Create a FastAPI app with:
   • A GET route /hello returning "Hello World"
2. Create an API to:
   • Add a product (name, price)
   • Get all products
3. Build a CRUD API for:
   • Books (title, author, price)
4. Modify the student API:
   • Add email field
   • Validate age should be greater than 5
5. Create an API endpoint:
   • /square/{num} → returns square of a number

---

Challenge Task

Build a Mini User Management API:

• Add user
• Get all users
• Update user
• Delete user
• Use Pydantic validation
• Handle errors properly