An API (Application Programming Interface) is a contract that lets programs talk to each other. A REST API uses HTTP to exchange data in JSON format.

Status codes

import requests

url = "https://api.open-meteo.com/v1/forecast"
params = {
    "latitude": 37.95,
    "longitude": -91.77,
    "current": "temperature_2m",
}

response = requests.get(url, params=params,
                        timeout=10)
response.raise_for_status()   # raise on 4xx/5xx

data = response.json()
temp = data["current"]["temperature_2m"]
print(f"Temperature: {temp}°C")

Navigating nested JSON

# Given: {"users": [{"name": "Alice", "scores": [92, 88]}]}

data = response.json()

# Chained access
name = data["users"][0]["name"]

# Safe access with .get()
email = data["users"][0].get("email", "N/A")

# Loop over array
for user in data.get("users", []):
    print(user["name"])

import os

# Store secrets in environment variables — never in code
api_key = os.environ["MY_API_KEY"]

# Bearer token
headers = {"Authorization": f"Bearer {api_key}"}

# X-API-Key header
headers = {"X-API-Key": api_key}

response = requests.get(url, headers=headers,
                        timeout=10)

POST with JSON body

payload = {
    "model": "gpt-4",
    "messages": [{"role": "user",
                  "content": "Hello"}]
}

response = requests.post(
    "https://api.openai.com/v1/chat/completions",
    headers={"Authorization": f"Bearer {api_key}"},
    json=payload,   # auto-encodes and sets Content-Type
    timeout=30,
)

Page-based pagination

results = []
page = 1

while True:
    r = requests.get(url, params={"page": page},
                     timeout=10)
    r.raise_for_status()
    data = r.json()
    items = data.get("results", [])
    if not items:
        break
    results.extend(items)
    page += 1

Exponential backoff retry

import time

def get_with_retry(url, retries=3):
    for attempt in range(retries):
        try:
            r = requests.get(url, timeout=10)
            r.raise_for_status()
            return r.json()
        except requests.RequestException as e:
            if attempt == retries - 1:
                raise
            time.sleep(2 ** attempt)   # 1, 2, 4 s