Networking in Python

diagram what the requests library is doing that a raw socket is not mermaid

  flowchart TD
  A["requests.get('https://host/path')"] --> B["DNS: host -> IP address"]
  B --> C["TCP connect to IP:443"]
  C --> D["TLS handshake: certificate, cipher, keys"]
  D --> E["write an HTTP request: method, path, headers"]
  E --> F["read the status line and headers"]
  F --> G["read the body -- length or chunked"]
  G --> H["decode: gzip, then the charset"]
  H --> I["a Response object"]
  C -.->|"this layer is all socket.send / socket.recv gives you"| J["bytes in order, no structure"]

The two ends of this picture are the same connection. A socket gives you bytes; everything above it -- finding the host, negotiating TLS, framing an HTTP message, decoding the body -- is work someone has to do. Writing it yourself is the reason to reach for a library, not a weakness of sockets.

What is networking?

Networking is how computers exchange data.

Key concepts:

• IP address: identifies a machine
• Port: identifies a program/service on that machine
• Protocol: rules for communication

Common protocols:

• TCP: reliable (web, SSH)
• UDP: fast, not guaranteed (streaming, DNS)
• HTTP/HTTPS: web protocol (built on TCP)

What you’ll learn here

• Make HTTP requests (APIs) using requests and urllib
• Work with JSON data
• Build a basic HTTP server
• Use sockets for low-level TCP communication
• Timeouts, retries, and error handling

Safety note

Always be careful when handling:

• user input from the internet
• authentication tokens
• opening ports on public machines

sketch Everything requests does above a raw socket p5.js Pause Restart

Both ends of this picture are the same connection. A socket gives you an ordered stream of bytes and nothing else -- finding the host, negotiating TLS, framing an HTTP message and decoding the body are all work somebody has to do. Writing that yourself is the reason to reach for a library, not a shortcoming of sockets.

Check yourself

pch.quizTag pch.quizDefaultTitle

1. What does a TCP socket actually guarantee?

   A Messages arrive whole and in order B Bytes arrive in order and intact, with no message boundaries C Each `send` matches one `recv` D Delivery within a time limit
   pch.quizShowAnswer

   B — Bytes arrive in order and intact, with no message boundaries — Measured elsewhere on this site: `sendall(b'HELLO')` then `sendall(b'WORLD')` read by `recv(4)` came back as `[b'HELL', b'O', b'WORL']`. Framing is the application's job.

2. Which of these does a raw socket NOT do for you?

   A Deliver bytes in order B Retransmit lost packets C Parse HTTP headers D Detect corruption
   pch.quizShowAnswer

   C — Parse HTTP headers — Ordering, retransmission and checksums are TCP's job. Everything protocol-shaped above that — HTTP framing, TLS, content decoding — is written on top.

3. What is the first thing `requests.get('https://host/path')` must do?

   A Open a socket B Resolve the hostname to an IP address C Send the headers D Negotiate TLS
   pch.quizShowAnswer

   B — Resolve the hostname to an IP address — You cannot connect to a name. DNS resolution happens first, then the TCP connection, then the TLS handshake, and only then does any HTTP get written.

4. Why use a `Session` for repeated calls to the same host?

   A It is required for HTTPS B It reuses the connection and shares headers and cookies C It makes calls asynchronous D It retries automatically
   pch.quizShowAnswer

   B — It reuses the connection and shares headers and cookies — Reusing the connection skips the TCP and TLS handshakes on every subsequent request, which is usually the dominant cost for small responses.

🧪 Try It Yourself

Exercise 1 – HTTP GET with urllib

pch.exerciseTag pch.exerciseTitle

Exercise 2 – Socket Connection

pch.exerciseTag pch.exerciseTitle

Exercise 3 – Resolve a Hostname

pch.exerciseTag pch.exerciseTitle