Code Explainers

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python 
import os
from pathlib import Path
 
BASE_DIR = Path(__file__).resolve().parent.parent.parent

How a Django settings module is wired

configuration environment-variables middleware
Intermediate 8 steps
rust 
use std::sync::OnceLock;
 
static CRC_TABLE: OnceLock<[u32; 256]> = OnceLock::new();
 

Table-driven CRC32 with lazy init in Rust

checksums lazy-initialization lookup-tables
Intermediate 8 steps
typescript 
import { parsePhoneNumberFromString, CountryCode } from 'libphonenumber-js';
 
export interface NormalizedPhone {
  e164: string;

Normalizing phone numbers to E.164 in TypeScript

validation normalization error-handling
Intermediate 7 steps
java 
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Map;
 

Evaluating math expressions with two stacks

stacks parsing operator-precedence
Intermediate 9 steps
ruby 
class Order < ApplicationRecord
  include AASM
 
  belongs_to :warehouse

Modeling an order lifecycle with AASM in Rails

state machine guards callbacks
Intermediate 10 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Broadcasting typing indicators in Laravel

websockets authorization presence-channels
Intermediate 9 steps
go 
func UploadChunk(c *gin.Context) {
	uploadID := c.Param("uploadID")
	if !validUploadID.MatchString(uploadID) {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid upload id"})

Resumable chunked uploads in Gin

file-upload content-range streaming
Advanced 9 steps
ruby 
require "timeout"
require "net/http"
 
class RemoteInventoryClient

Bounding a slow HTTP call with Timeout in Ruby

timeout error-handling http
Intermediate 6 steps
rust 
use axum::{
    body::Body,
    extract::Path,
    http::{header, HeaderMap, HeaderValue, StatusCode},

HTTP range requests for video streaming in Axum

http-range-requests streaming async-io
Advanced 8 steps
java 
@Entity
@Table(name = "orders")
@SQLDelete(sql = "UPDATE orders SET deleted = true, deleted_at = now() WHERE id = ?")
@Where(clause = "deleted = false")

Soft deletes with Hibernate in Spring

soft-delete jpa hibernate
Intermediate 9 steps
javascript 
import { useState, useEffect, useCallback } from 'react';
 
function getColumnCount(width) {
  if (width < 640) return 1;

A responsive column hook in React

custom-hooks debouncing responsive-design
Intermediate 7 steps
php 
<?php
 
namespace App\Services\Reports;
 

Streaming a monthly revenue CSV in Laravel

csv-export lazy-collections eloquent-query
Intermediate 8 steps
python 
def is_valid_card_number(number: str) -> bool:
    digits = [int(c) for c in number if c.isdigit()]
 
    if len(digits) < 13 or len(digits) > 19:

Validating card numbers with the Luhn check

checksum validation luhn-algorithm
Intermediate 6 steps
go 
func (h *ArticleHandler) Create(c *gin.Context) {
	var req struct {
		Title   string `json:"title" binding:"required"`
		Body    string `json:"body" binding:"required"`

Handling a POST request in Gin

request binding validation http status codes
Intermediate 7 steps
typescript 
import {
  CanActivate,
  ExecutionContext,
  Injectable,

Role-based access with a NestJS guard

authorization guards decorators
Intermediate 6 steps
ruby 
require "base64"
require "json"
 
module Attachment

Packing binary attachments into JSON

serialization base64 json
Intermediate 8 steps
rust 
use std::sync::mpsc;
use std::thread;
use std::time::Duration;
 

Running work with a timeout in Rust

concurrency channels timeout
Intermediate 7 steps
java 
@GetMapping("/files/{id}")
public ResponseEntity<StreamingResponseBody> download(
        @PathVariable String id,
        @RequestHeader(value = HttpHeaders.RANGE, required = false) String rangeHeader) throws IOException {

HTTP range requests in Spring

http-range streaming file-io
Advanced 10 steps