Python code explainers

python

import argparse
import sys
from pathlib import Path

Building a subcommand CLI with argparse

cli argparse subcommands

Intermediate 6 steps

python

from collections.abc import Mapping
from typing import Any, Iterator

Flattening nested config into dotted keys

recursion generators tree-traversal

Intermediate 7 steps

python

import csv
import io
from datetime import datetime

Streaming a CSV export in Flask

streaming generators csv

Intermediate 9 steps

python

import time
from collections import defaultdict
from threading import Lock

Sliding-window login rate limiting in Flask

rate-limiting sliding-window thread-safety

Intermediate 7 steps

python

from django.conf import settings
from django.contrib.auth import get_user_model
from django.core.mail import EmailMultiAlternatives
from django.db.models.signals import post_save

Sending a welcome email with Django signals

signals email user-activation

Intermediate 8 steps

python

import csv
import io
from datetime import date

Streaming a CSV export in FastAPI

streaming async-generators csv

Advanced 8 steps

python

import json
import logging
 
import stripe

Handling Stripe webhooks in Django

webhooks signature-verification idempotency

Intermediate 7 steps

python

from collections import deque
 
 
class RollingAverage:

A rolling average over a fixed window

sliding-window running-sum deque

Intermediate 7 steps

python

from collections import OrderedDict
from typing import Callable, Hashable, Iterable, Iterator, TypeVar
 
T = TypeVar("T")

Two ways to dedupe while keeping order

deduplication generators ordered-data

Intermediate 7 steps

python

from django.db.models import Sum, Count, F, DecimalField
from django.db.models.functions import TruncMonth, Coalesce
 
from .models import Order

Build a monthly revenue report in Django

aggregation orm group-by

Advanced 7 steps

python

from pathlib import Path
 
 
def print_tree(root, prefix="", show_hidden=False):

Printing a directory tree with recursion

recursion filesystem sorting

Intermediate 6 steps

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