lecture.md

Lecture 14: APIs & Requests

An Application Programming Interface (API) allows different software applications to communicate with each other over the web. Most web APIs use the HTTP protocol and exchange data in the JSON format.

---

1. How Web APIs Work

When you make a request to a web server (like typing a URL into a browser), the server responds.

• Client: Your program making the request.
• Server: The remote computer listening for requests and returning responses.
• HTTP Methods:
  • GET: Retrieve data from the server.
  • POST: Send new data to the server.
  • PUT/PATCH: Update existing data on the server.
  • DELETE: Remove data from the server.
• Status Codes:
  • 200 OK: Request succeeded.
  • 201 Created: Resource successfully created.
  • 400 Bad Request: The server could not understand the request.
  • 404 Not Found: The requested resource does not exist.
  • 500 Internal Server Error: The server encountered an error.

---

2. Using the requests Library (Third-Party)

The most popular way to make HTTP requests in Python is the requests library. First, install it:

pip install requests

Making a GET Request:

import requests

response = requests.get("https://api.github.com/users/octocat")

# Check status code
if response.status_code == 200:
    # Parse JSON response
    data = response.json()
    print(data["name"])      # Output: The Octocat
    print(data["company"])   # Output: GitHub
else:
    print(f"Failed to fetch data: {response.status_code}")

---

3. Using the Standard Library (urllib.request)

If you want to make requests without installing third-party libraries, you can use Python's built-in urllib module:

import urllib.request
import json

url = "https://api.github.com/users/octocat"
# Add a User-Agent header so GitHub doesn't block the request
req = urllib.request.Request(url, headers={'User-Agent': 'Python Study Client'})

try:
    with urllib.request.urlopen(req) as response:
        if response.status == 200:
            raw_data = response.read()
            data = json.loads(raw_data.decode("utf-8"))
            print(data["name"])
except Exception as e:
    print(f"Error occurred: {e}")

---

🧠 Try It Yourself

1. Use the public API https://jsonplaceholder.typicode.com/todos/1 to fetch a sample todo item and print its title.
2. Experiment with handling exceptions in case the API endpoint is down or returning a 404 status.