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System design patterns

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

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Builder pattern for mocking complex objects in Python

Use a fluent Builder to construct realistic mock objects with defaults, enabling readable test data setup.

class User:
    def __init__(self):
        self.name = "default"
        self.age = 0
        self.email = "unknown@example.com"
        self.address = "unknown"

    def __repr__(self):
        return f"User(name={self.name!r}, age={self.age}, email={self.email!r}, address={self.address!r})"


class UserBuilder:
   …

15 0 Open

System design patterns easy

How to Aggregate Mock API Routes by Method in Python

Groups mock API routes by path and method, collecting response bodies and counts into a nested dictionary structure.

defaultdict api-gateway aggregation

Python

from collections import defaultdict


def aggregate_mock_routes(routes):
    """Aggregate mock API routes by method and aggregate their response bodies."""
    aggregated = defaultdict(lambda: defaultdict(list))

    for route in routes:
        method = route["method"]
        path = route["path"]
        response = …

13 0 Open

System design patterns medium

How to Build an Adapter to Translate External API Responses in Python

Build an adapter class that translates a mock external API's response shape into your internal representation, keeping callers decoupled from the external contract.

adapter-pattern api architecture

Python

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

System design patterns medium

How to Migrate a Legacy Facade with the Strangler Fig Pattern in Python

Use a facade to wrap a legacy API and incrementally migrate callers to a modern interface, following the strangler fig pattern.

facade legacy migration

Python

class LegacyAPI:
    """Simulates the legacy system's raw interface."""
    def get_user(self, user_id):
        return {"id": user_id, "name": "Alice", "legacy": True}


class UserService:
    """Facade that wraps the legacy system with a modern interface."""
    def __init__(self, legacy_api=None):
        self.lega…

12 0 Open

System design patterns easy

How to Mock the Ambassador Pattern Retry Client in Python

This code demonstrates the ambassador pattern for API clients by simulating a flaky request and retrying with exponential backoff, useful for testing resilience in system design.

retry ambassador-pattern mock

Python

import time
import random


class RetryingClient:
    """Retry wrapper simulating a flaky ambassador-style API client."""

    def __init__(self, max_attempts=3, base_delay=0.1):
        self.max_attempts = max_attempts
        self.base_delay = base_delay
        self.attempts = 0

    def _flaky_request(self):
     …

15 0 Open

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