HTTP Explained¶

HTTP (HyperText Transfer Protocol) is how browsers and apps talk to servers. Every time you visit a website or call an API, you're using HTTP.

Learn Your Way¶

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Visualize It¶

See how Python builds and parses JSON, the data format used by most APIs: Open in Python Tutor

The request-response cycle¶

Your code sends a request to a server.
The server processes it and sends back a response.

Client                          Server
  |                               |
  |--- GET /posts/1 ------------>|
  |                               | (looks up post #1)
  |<-- 200 OK + JSON data -------|
  |                               |

HTTP methods¶

Method	Purpose	Example
`GET`	Read data	Get a list of users
`POST`	Create new data	Create a new user
`PUT`	Replace data entirely	Update all user fields
`PATCH`	Update part of data	Change just the email
`DELETE`	Remove data	Delete a user

Status codes¶

The server tells you what happened with a number:

Range	Meaning	Common codes
2xx	Success	200 OK, 201 Created, 204 No Content
3xx	Redirect	301 Moved Permanently, 304 Not Modified
4xx	Client error (your fault)	400 Bad Request, 401 Unauthorized, 404 Not Found
5xx	Server error (their fault)	500 Internal Server Error, 503 Service Unavailable

Headers¶

Extra information attached to requests and responses:

import requests

# Request headers — tell the server about your request.
response = requests.get(
    "https://api.example.com/data",
    headers={
        "Authorization": "Bearer your-token-here",
        "Accept": "application/json",
        "User-Agent": "my-python-app/1.0",
    }
)

# Response headers — the server tells you about the response.
print(response.headers["Content-Type"])    # "application/json"
print(response.headers["Content-Length"])   # "1234"

Request body¶

POST and PUT requests often send data in the body:

import requests

# Sending JSON data.
response = requests.post(
    "https://api.example.com/users",
    json={"name": "Alice", "email": "alice@example.com"},
)

Query parameters¶

Extra data in the URL after ?:

https://api.example.com/users?page=2&limit=10&sort=name

response = requests.get(
    "https://api.example.com/users",
    params={"page": 2, "limit": 10, "sort": "name"},
)

JSON — the language of APIs¶

Most APIs send and receive JSON (JavaScript Object Notation):

{
    "id": 1,
    "name": "Alice",
    "email": "alice@example.com",
    "is_active": true,
    "tags": ["admin", "user"]
}

Python dictionaries map directly to JSON:

response = requests.get("https://api.example.com/users/1")
data = response.json()    # Parse JSON → Python dict
print(data["name"])        # "Alice"

Common mistakes¶

Not checking status codes:

# Bad — assumes success.
data = requests.get(url).json()

# Good — check first.
response = requests.get(url)
if response.status_code == 200:
    data = response.json()
else:
    print(f"Error: {response.status_code}")

Not setting timeouts:

# Bad — waits forever if the server is down.
requests.get(url)

# Good — give up after 10 seconds.
requests.get(url, timeout=10)

Practice¶

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