Python code explainers

python

from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, status
from pydantic import BaseModel, EmailStr
from sqlalchemy.orm import Session

Building a signup endpoint in FastAPI

dependency-injection request-validation background-tasks

Intermediate 8 steps

python

from django import forms
from django.utils import timezone
 
from .models import Reservation

Multi-field validation in a Django ModelForm

form validation cross-field validation modelform

Intermediate 7 steps

python

from django import template
from django.urls import reverse, NoReverseMatch
from django.utils.html import format_html

Active nav-link template tags in Django

template tags url routing active state

Intermediate 7 steps

python

from functools import wraps
import asyncio
 
from fastapi import APIRouter, FastAPI, Request

Per-route request timeouts in FastAPI

decorators async timeouts

Intermediate 6 steps

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

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

python

from django.db.models import Q
 
from .models import Order

DISTINCT ON queries in Django

orm querysets postgresql

Intermediate 7 steps

python

import signal
import time
import logging

Graceful shutdown in a queue worker

signals graceful-shutdown message-queue

Intermediate 7 steps

python

from functools import lru_cache
 
 
class SpellingSuggester:

A spelling suggester with edit distance

edit-distance dynamic-programming memoization

Intermediate 9 steps

python

import asyncio
import json
 
from fastapi import APIRouter, Depends, HTTPException

Streaming export progress with SSE in FastAPI

server-sent-events async-generators streaming

Advanced 8 steps

python

from decimal import Decimal, ROUND_HALF_UP
 
from django.db import transaction
from django.db.models import F

Batch price updates safely in Django

decimal-precision batch-processing transactions

Advanced 8 steps

python

from django.db import transaction
from django.forms import inlineformset_factory
from django.shortcuts import get_object_or_404, redirect, render

Editing an order with inline formsets in Django

formsets transactions crud

Intermediate 9 steps

python

from flask import Blueprint, render_template, jsonify, request, abort
 
from .models import Article

Content negotiation in a Flask Blueprint

content-negotiation http-headers routing

Intermediate 7 steps

python

import os
import shutil
import tempfile
from contextlib import contextmanager

Transactional file operations in Python

transactions rollback closures

Intermediate 8 steps

python

from django.core.paginator import Paginator
from django.shortcuts import render
 
from .models import Product

Filtering and paginating a Django product list

queryset pagination filtering

Intermediate 7 steps

python

from werkzeug.routing import BaseConverter, ValidationError
from flask import Flask, jsonify, abort

Custom URL converters in Flask

url-routing validation converters

Intermediate 6 steps

python

from typing import List, Tuple
 
 
def merge_intervals(intervals: List[Tuple[int, int]]) -> List[Tuple[int, int]]:

How interval merging works

sorting greedy intervals

Intermediate 6 steps

python

import base64
import hashlib
import hmac
import os

How TOTP two-factor codes work

totp hmac authentication

Intermediate 7 steps