ABC TO XYZ OF AI

✅ Usecase1 using FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Welcome to my API!"}

@app.get("/items/{item_id}")
def read_item(item_id: int, q: str = None):
    return {"item_id": item_id, "query": q}

To run it:

uvicorn main:app --reload

→ Visit http://127.0.0.1:8000/docs for auto-generated Swagger UI.

🧠 Summary

Usecase 2

⚙️ Step 1: A Simple RESTful API Example

# file: main.py
from fastapi import FastAPI

app = FastAPI()

# Sample database (in memory)
users = {
    1: {"id": 1, "name": "Rajeev", "age": 30},
    2: {"id": 2, "name": "Priya", "age": 28}
}

# ✅ GET method - Read user
@app.get("/users/{user_id}")
def get_user(user_id: int):
    user = users.get(user_id)
    if user:
        return user
    return {"error": "User not found"}

# ✅ POST method - Create user
@app.post("/users")
def create_user(user: dict):
    new_id = max(users.keys()) + 1
    user["id"] = new_id
    users[new_id] = user
    return {"message": "User created", "user": user}

🧠 Step 2: What Happens Behind the Scenes

🔹 Example 1 — GET /users/1

Request (from client → server):

GET /users/1 HTTP/1.1
Host: localhost:8000

Response (server → client):

{
  "id": 1,
  "name": "Rajeev",
  "age": 30
}

🧩 What This Shows

🔹 Example 2 — POST /users

Request:

POST /users HTTP/1.1
Content-Type: application/json

{
  "name": "Asha",
  "age": 25
}

Response:

{
  "message": "User created",
  "user": {
    "id": 3,
    "name": "Asha",
    "age": 25
  }
}

🧩 What This Shows

🌐 REST Principles Illustrated

✅ Client–Server separation → Client requests, server responds.
✅ Statelessness → Every request is independent.
✅ Uniform Interface → Standard HTTP verbs (GET, POST, etc.)
✅ Representation → Data exchanged as JSON.
✅ Transfer → Done over HTTP.

Usecase3 ✅ — we’ll now build a full RESTful API example that supports all CRUD operations
(Create, Read, Update, Delete) in both FastAPI and Flask,
while clearly showing where Representational, State, and Transfer apply.

🚀 PART 1: FastAPI – Full REST Example

# file: fastapi_rest.py
from fastapi import FastAPI, HTTPException

app = FastAPI()

# In-memory "database"
users = {
    1: {"id": 1, "name": "Rajeev", "age": 30},
    2: {"id": 2, "name": "Priya", "age": 28}
}

# 🟩 CREATE (POST)
@app.post("/users")
def create_user(user: dict):
    new_id = max(users.keys()) + 1 if users else 1
    user["id"] = new_id
    users[new_id] = user
    return {"message": "User created", "user": user}

# 🟦 READ (GET)
@app.get("/users/{user_id}")
def get_user(user_id: int):
    if user_id not in users:
        raise HTTPException(status_code=404, detail="User not found")
    return users[user_id]

# 🟨 UPDATE (PUT - full replace)
@app.put("/users/{user_id}")
def update_user(user_id: int, new_data: dict):
    if user_id not in users:
        raise HTTPException(status_code=404, detail="User not found")
    new_data["id"] = user_id
    users[user_id] = new_data
    return {"message": "User replaced", "user": new_data}

# 🟧 PARTIAL UPDATE (PATCH)
@app.patch("/users/{user_id}")
def patch_user(user_id: int, partial_data: dict):
    if user_id not in users:
        raise HTTPException(status_code=404, detail="User not found")
    users[user_id].update(partial_data)
    return {"message": "User partially updated", "user": users[user_id]}

# 🟥 DELETE
@app.delete("/users/{user_id}")
def delete_user(user_id: int):
    if user_id not in users:
        raise HTTPException(status_code=404, detail="User not found")
    del users[user_id]
    return {"message": f"User {user_id} deleted"}

Run this app:

uvicorn fastapi_rest:app --reload

You can test all endpoints at 👉 http://127.0.0.1:8000/docs (auto-generated Swagger UI 🎯)

⚙️ How REST Concepts Apply

🧩 Representational · State · Transfer Summary

🐍 PART 2: Flask – Same REST Example

# file: flask_rest.py
from flask import Flask, jsonify, request

app = Flask(__name__)

users = {
    1: {"id": 1, "name": "Rajeev", "age": 30},
    2: {"id": 2, "name": "Priya", "age": 28}
}

# 🟩 CREATE
@app.route("/users", methods=["POST"])
def create_user():
    user = request.get_json()
    new_id = max(users.keys()) + 1 if users else 1
    user["id"] = new_id
    users[new_id] = user
    return jsonify({"message": "User created", "user": user}), 201

# 🟦 READ
@app.route("/users/<int:user_id>", methods=["GET"])
def get_user(user_id):
    user = users.get(user_id)
    if not user:
        return jsonify({"error": "User not found"}), 404
    return jsonify(user)

# 🟨 UPDATE
@app.route("/users/<int:user_id>", methods=["PUT"])
def update_user(user_id):
    if user_id not in users:
        return jsonify({"error": "User not found"}), 404
    new_data = request.get_json()
    new_data["id"] = user_id
    users[user_id] = new_data
    return jsonify({"message": "User replaced", "user": new_data})

# 🟧 PARTIAL UPDATE
@app.route("/users/<int:user_id>", methods=["PATCH"])
def patch_user(user_id):
    if user_id not in users:
        return jsonify({"error": "User not found"}), 404
    partial_data = request.get_json()
    users[user_id].update(partial_data)
    return jsonify({"message": "User partially updated", "user": users[user_id]})

# 🟥 DELETE
@app.route("/users/<int:user_id>", methods=["DELETE"])
def delete_user(user_id):
    if user_id not in users:
        return jsonify({"error": "User not found"}), 404
    del users[user_id]
    return jsonify({"message": f"User {user_id} deleted"})

Run this app:

python flask_rest.py

Then open 👉 http://127.0.0.1:5000/users/1 to test endpoints via Postman or curl.

⚡ Difference Summary: FastAPI vs Flask

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