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System design patterns

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

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Create a Data Helper Class in Python

A reusable DataHelper class that saves and loads JSON and CSV files from a configurable base directory, with automatic header detection for CSV.

data-helper json csv

Python

import json
import csv
from pathlib import Path

class DataHelper:
    def __init__(self, base_path="."):
        self.base_path = Path(base_path)
        self.base_path.mkdir(exist_ok=True)

    def save_json(self, data, filename):
        path = self.base_path / filename
        with open(path, "w") as f:
          …

15 0 Open

System design patterns medium

Facade Pattern in Python with Mock Simplification

This code demonstrates the Facade pattern by hiding complex subsystem interactions behind a simple start/stop interface, and adds a MockFacade for testing failure scenarios.

facade-pattern design-patterns abstraction

Python

class SubsystemA:
    def operation_a(self):
        return "Subsystem A: ready"

class SubsystemB:
    def operation_b(self):
        return "Subsystem B: ready"

class SubsystemC:
    def operation_c(self):
        return "Subsystem C: ready"


class Facade:
    def __init__(self):
        self._a = SubsystemA()
   …

15 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

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