System design patterns

import json
from typing import Dict, Any


class ExternalAPI:
    """Mock external service returning a different data shape."""
    def get_user(self, user_id: int) -> Dict[str, Any]:
        return {
            "id": user_id,
            "full_name": "Jane Doe",
            "email_address": "jane@example.com",
     …

14 0 Open

value-object immutability money

How to Build an Immutable Money Value Object in Python

Implement an immutable Money class with rounded decimal amounts, currency, safe equality, and hashing for use as a value object.

class Money:
    def __init__(self, amount: float, currency: str):
        object.__setattr__(self, "_amount", round(amount, 2))
        object.__setattr__(self, "_currency", currency)

    def __setattr__(self, name, value):
        raise AttributeError(f"Money is immutable: cannot set '{name}'")

    def __delattr__…

cqrs dataclasses repositories

How to Implement CQRS with Separate Read and Write Models in Python

Implements Command Query Responsibility Segregation (CQRS) by splitting data into separate write and read models with dedicated repositories, using dataclasses for structure.

from dataclasses import dataclass, field
from typing import List, Dict, Optional


@dataclass
class OrderWriteModel:
    order_id: int
    customer: str
    items: List[str] = field(default_factory=list)

    def add_item(self, item: str) -> None:
        self.items.append(item)


@dataclass
class OrderReadModel:
    …

14 0 Open

abstract-factory design-patterns system-design

How to Implement the Abstract Factory Pattern in Python

Implements the Abstract Factory pattern to create families of related GUI objects (buttons, checkboxes) without specifying their concrete classes.

from abc import ABC, abstractmethod


class Button(ABC):
    @abstractmethod
    def render(self):
        pass


class Checkbox(ABC):
    @abstractmethod
    def render(self):
        pass


class WindowsButton(Button):
    def render(self):
        return "Rendering Windows-style button"


class WindowsCheckbox(Chec…

deduplication inbox-pattern dataclasses

Inbox pattern consumer dedupe mock in Python

Implements a mock inbox consumer that deduplicates incoming messages by ID, with automatic eviction of old seen IDs to prevent unbounded memory growth.

import json
from collections import deque
from dataclasses import dataclass, field
from hashlib import sha256
from typing import Any


@dataclass
class InboxConsumer:
    max_seen: int = 1000
    seen_ids: set = field(default_factory=set)
    seen_history: deque = field(default_factory=deque)

    def _mark_seen(self,…

microkernel plugin design-patterns

Microkernel Plug-in Core Mock in Python

Implements a minimal microkernel plug-in core that registers, unregisters, and executes synchronous or asynchronous plugins via a pluggable manager class.

import json
import abc
import inspect


class MicrokernelCore(abc.ABC):

    def __init__(self):
        self._plugins = {}

    def register(self, name, plugin):
        self._plugins[name] = plugin

    def unregister(self, name):
        return self._plugins.pop(name, None)

    def execute(self, name, *args, **kwa…

template-method design-patterns abc

Template Method Workflow Steps Base Class in Python

Define a reusable workflow skeleton in a base class and let subclasses fill in each step with the Template Method design pattern.

from abc import ABC, abstractmethod


class DataPipeline(ABC):
    """Template Method pattern: defines a workflow skeleton."""

    def run(self):
        """Template method - defines the algorithm's structure."""
        result = {"extracted": False, "transformed": False, "loaded": False}
        raw_data = self._ext…