Reference library

System design patterns

Sharding, load balancing, CAP tradeoffs, and scaling patterns — interview and production ready.

6 matches

How to Build an MVP Presenter View Mock in Python

A minimal MVP (Model-View-Presenter) mock showing a Presenter controlling a SlideDeck model with slide navigation and typed state via dataclasses.

dataclasses mvp design-patterns

Python

from dataclasses import dataclass, field
from typing import List


@dataclass
class SlideDeck:
    title: str
    slides: List[str] = field(default_factory=list)
    current_index: int = 0

    def next_slide(self) -> str:
        if self.current_index < len(self.slides) - 1:
            self.current_index += 1
      …

13 0 Open

System design patterns easy

How to Implement a Data Helper Class in Python

Build a beginner-friendly DataHelper class using dataclasses and key system design patterns like Command, Strategy, and Map.

dataclass data-helper design-patterns

Python

from __future__ import annotations
from dataclasses import dataclass, field
from typing import Any, Dict, List, Optional


@dataclass
class DataHelper:
    """A beginner-friendly data utility with common system design patterns."""
    data: List[Dict[str, Any]] = field(default_factory=list)

    def add_record(self, r…

13 0 Open

System design patterns easy

How to Implement a Simple Event Bus in Python

Create a publish-subscribe event bus using dataclasses and defaultdict to decouple event producers from consumers.

event-bus publish-subscribe design-patterns

Python

from collections import defaultdict
from dataclasses import dataclass, field
from typing import Callable, Dict, List, Set


@dataclass
class EventBus:
    _subscribers: Dict[str, List[Callable]] = field(
        default_factory=lambda: defaultdict(list)
    )

    def subscribe(self, event_type: str, handler: Callable…

15 0 Open

System design patterns easy

How to Implement the Prototype Pattern with Deep Copy in Python

Implements the Prototype design pattern using copy.deepcopy to clone complex objects without sharing mutable state.

prototype-pattern deepcopy dataclasses

Python

import copy
from dataclasses import dataclass, field
from typing import List

@dataclass
class Engine:
    horsepower: int

@dataclass
class Car:
    brand: str
    engine: Engine
    accessories: List[str] = field(default_factory=list)

def clone_prototype(car: Car) -> Car:
    return copy.deepcopy(car)

if __name__ …

13 0 Open

System design patterns easy

How to Mock a Metrics Decorator in Python with unittest.mock

This code demonstrates a timing decorator that wraps a function to measure execution time and prints the duration, with a unit test using unittest.mock to patch the print function and assert it was called.

decorators unittest.mock metrics

Python

import time
from functools import wraps
from unittest.mock import patch

def add_metrics(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        elapsed = time.perf_counter() - start
        print(f"{func.__name__} took {elapsed:.6f}s…

15 0 Open

System design patterns easy

Idempotent Consumer: Store Processed IDs in Python

Implement an idempotent consumer that persists processed message IDs to a JSON file, skipping duplicates on restart.

idempotency duplicate-detection state-persistence

Python

import json
from pathlib import Path


class IdempotentStore:
    def __init__(self, storage_path: str = "processed_ids.json"):
        self.storage_path = Path(storage_path)
        self.processed_ids = self._load()

    def _load(self) -> set:
        if self.storage_path.exists():
            with self.storage_path…

15 0 Open

Browse by section

Each section groups closely related Python snippets.