Python code explainers

python

import requests
from requests.adapters import HTTPAdapter
from urllib3.util.retry import Retry

Building a resilient requests Session

retries backoff http-client

Intermediate 7 steps

python

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

Building a users router in FastAPI

routing serialization dependency-injection

Intermediate 7 steps

python

import json
from dataclasses import dataclass, field, asdict
from datetime import datetime
from typing import Any

JSON round-tripping with Python dataclasses

dataclasses serialization json

Intermediate 6 steps

python

import re
 
from django.core.exceptions import ValidationError
from django.core.validators import RegexValidator

Building a deconstructible validator in Django

validation regex deconstructible

Intermediate 7 steps

python

from dataclasses import dataclass
from typing import Optional
 
from sqlalchemy import select, func

Building a pagination helper with SQLAlchemy

pagination dataclass computed-properties

Intermediate 8 steps

python

from datetime import timedelta
 
from django.contrib.sessions.models import Session
from django.core.management.base import BaseCommand

A batched session-cleanup command in Django

management-command batch-processing database-cleanup

Intermediate 7 steps

python

import re
from email_validator import validate_email, EmailNotValidError
 
_DISPOSABLE_DOMAINS = {

Normalizing signup emails in Python

validation normalization data-cleaning

Intermediate 8 steps

python

import time
from concurrent.futures import ThreadPoolExecutor, as_completed
from pathlib import Path

Parallel file downloads with a thread pool

concurrency thread-pool streaming-io

Intermediate 8 steps

python

from datetime import datetime
from zoneinfo import ZoneInfo

Timezone-safe datetime handling in Python

timezones datetime normalization

Intermediate 4 steps

python

import shutil
import uuid
from pathlib import Path

Safe avatar uploads in FastAPI

file-upload validation streaming

Intermediate 8 steps

python

from django.db.models import Prefetch, Count
from django.views.generic import ListView
 
from .models import Article, Comment

Building an efficient article list in Django

orm query-optimization prefetching

Intermediate 6 steps

python

from django.db import models
from django.utils.text import slugify

Auto-generating unique slugs in Django

slugs orm model-methods

Intermediate 7 steps

python

from functools import lru_cache
import math

Memoizing number theory with lru_cache

memoization number-theory caching

Intermediate 8 steps

python

import re
from collections import defaultdict
from pathlib import Path

Summarizing log files by date in Python

regex parsing aggregation

Intermediate 7 steps

python

import threading
import logging
 
logger = logging.getLogger(__name__)

A self-rescheduling periodic task in Python

threading scheduling concurrency

Intermediate 6 steps

python

from collections import ChainMap
from functools import reduce
from typing import Any, Iterable, Mapping

Five ways to merge dicts in Python

dictionaries merging recursion

Intermediate 8 steps

python

from fastapi import Depends, FastAPI, HTTPException
from sqlalchemy import create_engine
from sqlalchemy.orm import Session, sessionmaker

Wiring SQLAlchemy sessions into FastAPI

dependency-injection orm sessions

Intermediate 7 steps

python

import re
 
_UNIT_SECONDS = {
    "w": 604800,

Parsing duration strings like 1h30m in Python

regex parsing validation

Intermediate 8 steps