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System design patterns

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

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How to Implement a Simple MVVM Binding Mock in Python

A minimal Python implementation of the MVVM pattern, mocking data binding so views auto-update when the view model changes.

mvvm binding observer pattern

Python

class BindingMock:
    def __init__(self, view_model):
        self.view_model = view_model
        self.subscribers = []

    def bind(self, property_name, callback):
        self.subscribers.append((property_name, callback))

    def set(self, property_name, value):
        setattr(self.view_model, property_name, va…

18 0 Open

System design patterns medium

Mock Unit of Work commit and rollback in Python

Verify that a Unit of Work pattern commits on success and rolls back on failure using unittest.mock in Python.

unit-of-work mocking testing

Python

from unittest import mock


class UnitOfWork:
    def __init__(self):
        self.committed = False
        self.rolled_back = False

    def commit(self):
        self.committed = True
        print("Commit executed")

    def rollback(self):
        self.rolled_back = True
        print("Rollback executed")


def b…

13 0 Open

System design patterns medium

Object Pool Pattern for Database Connections in Python

Implements a reusable connection pool with acquire/release and context manager support, mocking database connections with idle reuse and exhaustion handling.

object-pool connection-pool databases

Python

import time
from contextlib import contextmanager
from collections import deque


class ConnectionPool:
    def __init__(self, size=3, max_idle=5):
        self._idle = deque(maxlen=max_idle)
        self._active = set()
        self.size = size

    def _create(self):
        return {"created_at": time.time(), "queri…

12 0 Open

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