An API (application programming interface) is a contract that lets programs talk to each other. A REST-style web API uses HTTP endpoints to exchange structured data, often JSON.

HTTP Method	Action
GET	Read data
POST	Create data
PUT	Replace data
PATCH	Update part of data
DELETE	Remove data

Status codes

Code	Meaning
200	OK — success
201	Created
400	Bad request
401	Unauthorized
404	Not found
429	Rate limited
500	Server error

import requests

url = "https://api.example.test/weather"
params = {"city": "Chicago", "units": "fahrenheit"}

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

data = response.json()
print(data["temperature"])

Offline-safe fixtures

class DemoResponse:
    def __init__(self, payload, status_code=200):
        self._payload = payload
        self.status_code = status_code

    def raise_for_status(self):
        if self.status_code >= 400:
            raise requests.HTTPError(self.status_code)

    def json(self):
        return self._payload

response = DemoResponse({"temperature": 72.5})

A response body arrives as text. response.json() calls json.loads() on it for you.

Function	Converts
json.loads(text)	JSON string to dict / list
json.dumps(obj)	dict / list to JSON string

JSON	Python
"text" (double quotes only)	'text' or "text"
true, false	True, False
null	None

import json

raw_body = '{"city": "Chicago", "raining": false, "alerts": null}'
weather = json.loads(raw_body)
print(weather["raining"], weather["alerts"])
print(weather.get("humidity", "not reported"))

summary_text = json.dumps({"city": weather["city"],
                           "raining": weather["raining"]})
print(summary_text)

False None
not reported
{"city": "Chicago", "raining": false}

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 = {
    "name": "Alice",
    "role": "student",
}

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

Defensive parsing

payload = {
    "user": {
        "profile": {"department": "Analytics"}
    }
}

department = (
    payload
    .get("user", {})
    .get("profile", {})
    .get("department", "unknown")
)

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