Code Explainers

Browse the library

python 
from django.contrib.auth.mixins import LoginRequiredMixin
from django.views.generic import ListView
 
from .models import Invoice

Building a scoped, filtered ListView in Django

class-based views queryset filtering authentication
Intermediate 7 steps
java 
public class GitHubUserClient {
 
    private final HttpClient http = HttpClient.newBuilder()
            .connectTimeout(Duration.ofSeconds(10))

Calling the GitHub API with Java's HttpClient

http-client json-deserialization error-handling
Intermediate 9 steps
ruby 
require "yaml"
require "pathname"
 
class AppConfig

A typed config loader in Ruby

yaml configuration recursion
Intermediate 8 steps
javascript 
function splitFullName(fullName) {
  const cleaned = (fullName || '').trim().replace(/\s+/g, ' ');
 
  if (!cleaned) {

Parsing full names into first and last

string-parsing regex edge-cases
Intermediate 8 steps
php 
<?php
 
namespace App\Providers;
 

Defining rate limiters in Laravel

rate limiting service provider closures
Intermediate 7 steps
rust 
use axum::{
    async_trait,
    body::Bytes,
    extract::FromRequest,

A strict JSON extractor in Axum

extractors traits content-negotiation
Advanced 7 steps
typescript 
export class Semaphore {
  private available: number;
  private readonly waiters: Array<() => void> = [];
 

Building an async Semaphore in TypeScript

concurrency async-await promises
Advanced 6 steps
go 
package checksum
 
import (
	"crypto/sha256"

Computing SHA-256 checksums in Go

hashing io-streaming filesystem-walk
Intermediate 7 steps
python 
import click
 
 
@click.command()

Building a typed CLI with Click

cli decorators validation
Intermediate 7 steps
java 
public final class AccessLogParser {
 
    private static final Pattern LINE = Pattern.compile(
        "^(?<ip>\\S+) \\S+ \\S+ \\[(?<time>[^\\]]+)\\] "

Parsing Apache access logs in Java

regex named-groups parsing
Intermediate 7 steps
ruby 
module ProductsHelper
  def cached_product_row(product)
    cache [product, current_user.role] do
      render partial: "products/row", locals: { product: product }

Russian doll caching that busts itself in Rails

fragment-caching cache-invalidation associations
Intermediate 4 steps
go 
package dateutil
 
import (
	"fmt"

Parsing and formatting dates in Go

date parsing layouts timezones
Intermediate 7 steps
java 
public class KeysetPaginationRepository {
 
    private final DataSource dataSource;
 

How keyset pagination works in Java

pagination sql jdbc
Intermediate 8 steps
typescript 
import { IsInt, IsOptional, Max, Min } from 'class-validator';
import { Type } from 'class-transformer';
 
export class PaginationQueryDto {

Type-safe pagination queries in NestJS

pagination validation dto
Intermediate 7 steps
javascript 
import { db } from '@/lib/db'
 
const SITE_URL = process.env.NEXT_PUBLIC_SITE_URL ?? 'https://example.com'
 

Generating a dynamic sitemap in Next.js

sitemap seo database-query
Intermediate 5 steps
ruby 
def build_pivot_table(sales)
  pivot = sales.each_with_object(Hash.new { |h, k| h[k] = Hash.new(0.0) }) do |record, table|
    region = record.fetch(:region)
    quarter = record.fetch(:quarter)

Building a pivot table in Ruby

aggregation nested-hashes default-values
Intermediate 9 steps
python 
import csv
 
from django.http import StreamingHttpResponse
from django.utils.timezone import now

Streaming a CSV export in Django

streaming csv-export generators
Intermediate 7 steps
php 
<?php
 
function fetchAll(array $urls, int $concurrency = 10, int $timeout = 15): array
{

Bounded-concurrency HTTP fetching with curl_multi

concurrency http curl
Advanced 8 steps