Python code explainers

python

from dataclasses import dataclass, fields, MISSING
from typing import get_type_hints, get_origin, get_args, Union

Type-checking dataclasses at runtime

dataclasses type-hints runtime-validation

Advanced 8 steps

python

import time
import threading

How a thread-safe token bucket rate limiter works

rate-limiting concurrency locking

Intermediate 6 steps

python

from flask import Blueprint, render_template, redirect, url_for, flash
from flask_login import login_required, current_user
from flask_wtf import FlaskForm
from wtforms import StringField, TextAreaField, SubmitField

Handling a post form with a Flask Blueprint

blueprints form-validation post-redirect-get

Intermediate 7 steps

python

import random
import time
import logging
from functools import wraps

A retry decorator with exponential backoff

decorators retry exponential-backoff

Intermediate 6 steps

python

from django.db import models
from django.utils import timezone

How soft deletes work in Django

soft-delete querysets managers

Intermediate 10 steps

python

from functools import wraps
 
 
def memoize(func):

Building a memoize decorator in Python

decorators closures memoization

Intermediate 5 steps

python

import os
import tempfile
from pathlib import Path
from typing import Union

How atomic file writes work in Python

atomicity filesystem durability

Advanced 7 steps

python

import re
from datetime import datetime
from dataclasses import dataclass

Parsing access logs with named regex groups

regex named-groups dataclasses

Intermediate 6 steps

python

import gzip
from pathlib import Path
from typing import Iterator

Streaming TSV records with Python generators

generators lazy-evaluation file-io

Intermediate 5 steps

python

import hashlib
import hmac
import os

Verifying signed payment webhooks in Flask

hmac webhooks signature verification

Intermediate 7 steps

python

from flask import Blueprint, render_template, request, abort
from sqlalchemy import select
 
from .models import Article

Paginating articles in a Flask Blueprint

pagination blueprints input-validation

Intermediate 6 steps

python

from fastapi import APIRouter, Depends, Query
from pydantic import BaseModel
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

How a paginated list endpoint works in FastAPI

pagination dependency-injection async-orm

Intermediate 8 steps

python

from fastapi import FastAPI, Request, status
from fastapi.responses import JSONResponse
 
app = FastAPI()

Custom exception handlers in FastAPI

exception handling error responses separation of concerns

Intermediate 7 steps

python

class FileManager:
    """A context manager that safely opens and closes a file."""
 
    def __init__(self, path, mode="r"):

Writing context managers in Python

context-managers resource-management exception-handling

Intermediate 6 steps

python

from collections import deque
 
 
def bfs(graph, start):

Breadth-first search and shortest paths in Python

graph-traversal bfs queue

Intermediate 9 steps

python

class Typed:
    """A data descriptor that enforces a type and optional validation."""
 
    def __init__(self, expected_type, validator=None):

Building a typed descriptor in Python

descriptors validation metaprogramming

Advanced 8 steps

python

from collections import Counter
 
 
def word_frequencies(text):

Counting things with collections.Counter

counting multiset data-structures

Beginner 8 steps

python

def two_sum_sorted(numbers, target):
    """Find indices of two values that sum to target in a sorted array."""
    left, right = 0, len(numbers) - 1
    while left < right:

Two-pointer search on sorted arrays

two-pointers arrays sorting

Intermediate 9 steps