API Basics¶

An API (Application Programming Interface) is a way for programs to talk to each other. When people say "API" in web development, they usually mean a web API — a server that accepts HTTP requests and returns data (usually JSON).

Learn Your Way¶

Read	Build	Watch	Test	Review	Visualize
You are here	Projects	Videos	Quiz	Flashcards	Diagrams

Visualize It¶

See how Python works with JSON data, the format APIs use to communicate: Open in Python Tutor

How APIs work¶

Your Python script          The API server
       |                          |
       |-- GET /posts ----------->|
       |                          | (looks up posts in database)
       |<-- 200 OK + JSON --------|
       |                          |

Your script is the client. The API is the server. The conversation happens over HTTP.

REST — the most common API style¶

REST (Representational State Transfer) is a set of conventions for designing APIs:

Action	HTTP Method	URL	Example
List all	GET	`/users`	Get all users
Get one	GET	`/users/42`	Get user #42
Create	POST	`/users`	Create a new user
Update	PUT	`/users/42`	Replace user #42
Delete	DELETE	`/users/42`	Delete user #42

The URL identifies the resource (what you're working with). The HTTP method identifies the action (what you're doing to it).

Making API calls with Python¶

import requests

# GET — read data.
response = requests.get("https://jsonplaceholder.typicode.com/posts/1")
post = response.json()
print(post["title"])

# POST — create data.
new_post = {"title": "My Post", "body": "Content here", "userId": 1}
response = requests.post(
    "https://jsonplaceholder.typicode.com/posts",
    json=new_post,
)
print(response.status_code)    # 201 Created

Building APIs with Python¶

FastAPI lets you create APIs:

from fastapi import FastAPI

app = FastAPI()

@app.get("/hello/{name}")
def hello(name: str):
    return {"message": f"Hello, {name}!"}

Run with uvicorn app:app and visit http://localhost:8000/hello/Alice.

Authentication¶

Most APIs require you to prove who you are:

API Key — a secret string you include in the request:

response = requests.get(url, headers={"X-API-Key": "your-key-here"})

Bearer Token (JWT) — a token you get by logging in:

response = requests.get(url, headers={"Authorization": "Bearer eyJ..."})

Common public APIs for practice¶

API	URL	What it provides
JSONPlaceholder	jsonplaceholder.typicode.com	Fake posts, users, comments
Open Meteo	open-meteo.com	Weather data
PokéAPI	pokeapi.co	Pokémon data
REST Countries	restcountries.com	Country information

These are free, require no API key, and are safe to practice with.

Common mistakes¶

Not handling errors:

# Bad — crashes if the API is down.
data = requests.get(url).json()

# Good — check the response first.
response = requests.get(url, timeout=10)
response.raise_for_status()    # Raises an exception for 4xx/5xx
data = response.json()

Hardcoding API URLs:

# Bad
requests.get("https://api.example.com/v2/users")

# Good — use a variable or config.
BASE_URL = "https://api.example.com/v2"
requests.get(f"{BASE_URL}/users")

Practice¶

Quick check: Take the quiz

Review: Flashcard decks Practice reps: Coding challenges

← Prev	Home	Next →