Working with APIs

Call REST APIs, read JSON responses, handle pagination, and build real programs powered by live internet data.

"An API is a restaurant menu: you don't go into the kitchen, you just say what you want and get back what you ordered. JSON is how the restaurant writes the receipt."

— Shurai

What is a REST API?

A REST API is a web service you talk to by sending HTTP requests to URLs (called endpoints). Each endpoint does one thing: get a list, create a record, update, or delete. The server replies with data — almost always in JSON format:

The four HTTP verbs — CRUD operations:

GET Read Fetch data. Never changes anything on the server. POST Create Send data to create a new resource. PUT Update Replace an existing resource entirely. DELETE Delete Remove a resource.

Calling a Real API — Step by Step

Let’s use JSONPlaceholder — a free practice API that mimics a real to-do app:

python

import requests

# 1. GET — fetch all todos
resp = requests.get("https://jsonplaceholder.typicode.com/todos")
todos = resp.json()
print(f"Total todos: {len(todos)}")            # 200

# 2. GET one item by ID
todo = requests.get("https://jsonplaceholder.typicode.com/todos/1").json()
print(todo)
# {'userId': 1, 'id': 1, 'title': 'delectus aut autem', 'completed': False}

# 3. POST — create a new todo
new_todo = {"title": "Learn Python APIs", "completed": False, "userId": 1}
resp     = requests.post("https://jsonplaceholder.typicode.com/todos", json=new_todo)
print(resp.status_code, resp.json())   # 201 {'id': 201, 'title': 'Learn...}

# 4. DELETE
resp = requests.delete("https://jsonplaceholder.typicode.com/todos/1")
print(resp.status_code)               # 200 — deleted

Parsing Nested JSON Like a Pro

Real API responses are often deeply nested. Treat the JSON like a Python dict — because it is one:

python — GitHub API example

import requests

resp = requests.get("https://api.github.com/repos/python/cpython")
repo = resp.json()

# Navigate nested keys just like a dict
print(repo["full_name"])           # python/cpython
print(repo["stargazers_count"])    # 60000+
print(repo["owner"]["login"])     # python  — nested dict
print(repo.get("homepage", "N/A")) # use .get() for optional keys

Handling Pagination

Most APIs return results in pages (e.g. 100 items per page). Loop through pages until you have everything:

python

import requests

def get_all_users():
    all_users = []
    page      = 1

    while True:
        resp = requests.get(
            "https://reqres.in/api/users",
            params={"page": page},
            timeout=5
        )
        data     = resp.json()
        all_users.extend(data["data"])
        if page >= data["total_pages"]:
            break
        page += 1

    return all_users

users = get_all_users()
print(f"Total users: {len(users)}")

Real Example — Currency Converter

python — using ExchangeRate-API (free tier)

import requests

def convert_currency(amount, from_cur, to_cur):
    """Convert amount from one currency to another."""
    url  = f"https://api.frankfurter.app/latest?from={from_cur}&to={to_cur}"
    try:
        resp = requests.get(url, timeout=5)
        resp.raise_for_status()
        rate     = resp.json()["rates"][to_cur]
        result   = amount * rate
        print(f"{amount} {from_cur} = {result:.2f} {to_cur} (rate: {rate})")
    except requests.exceptions.RequestException as e:
        print(f"Error: {e}")

convert_currency(1000, "INR", "USD")
convert_currency(100,  "USD", "EUR")
convert_currency(500,  "GBP", "JPY")

Finding APIs to practice with

Great free APIs with no key required: Open-Meteo (weather), Frankfurter.app (currency), JSONPlaceholder (fake CRUD), GitHub API (repos/users), REST Countries (country data). For premium APIs, look for a free tier — most have one.

"Once you understand REST + JSON, every app on the internet is a data source. News, sports scores, stock prices, maps — they all speak the same language."

— Shurai

🧠 Quiz — Q1

What does the GET HTTP verb do?

🧠 Quiz — Q2

An API returns JSON. After calling data = resp.json(), how do you access a nested field owner.login?

🧠 Quiz — Q3

Why should you use .get("key", default) when reading JSON response fields?

🧠 Quiz — Q4

What does pagination mean in the context of APIs?