socket — Low-level networking interface

The socket module provides access to the BSD socket interface. It is the foundation of all network communication in Python. While high-level libraries (like requests for HTTP or asyncio for scalable servers) are preferred for application development, understanding sockets is crucial for low-level network programming.

import socket

Creating a Simple TCP Client

A client creates a socket, connects to a remote address, sends data, and receives a response.

import socket

# 1. Create a socket object (IPv4, TCP)
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

try:
    # 2. Connect to the server
    s.connect(("example.com", 80))
    
    # 3. Send data (must be bytes)
    request = b"GET / HTTP/1.1\r\nHost: example.com\r\n\r\n"
    s.sendall(request)
    
    # 4. Receive data
    response = s.recv(4096)
    print(response.decode('utf-8'))
finally:
    # 5. Always close the socket!
    s.close()

Creating a Simple TCP Server

A server creates a socket, binds it to a local address and port, listens for incoming connections, and accepts them.

import socket

# Use a context manager to ensure the socket closes automatically
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    # Allow port reuse (prevents "Address already in use" error)
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    
    # 1. Bind to an address and port
    # Empty string means all available interfaces
    s.bind(('', 65432))
    
    # 2. Listen for connections (allow up to 5 pending connections)
    s.listen(5)
    print("Server listening on port 65432...")
    
    # 3. Accept a connection (This blocks until a client connects)
    conn, addr = s.accept()
    with conn:
        print(f"Connected by: {addr}")
        while True:
            # Receive data
            data = conn.recv(1024)
            if not data:
                break
            
            # Echo data back to client
            conn.sendall(data)

API Reference

Core Constants

Socket Methods