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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 Build a Sidecar Logging Proxy in Python

Wrap any object with a proxy that transparently logs every method call, arguments, return value, and execution time to a file — mimicking a sidecar pattern.

proxy logging sidecar

Python

import logging
import time
from datetime import datetime


class LoggingProxy:
    """Sidecar-style proxy that logs all calls to a wrapped object."""

    def __init__(self, target, log_file="proxy.log"):
        self._target = target
        logging.basicConfig(
            filename=log_file,
            level=loggin…

15 0 Open

System design patterns medium

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.

value-object immutability money

Python

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__…

13 0 Open

System design patterns medium

How to implement stale-while-revalidate caching in Python

A Python cache wrapper that returns a stale cached value with a fallback flag when the upstream fetch fails, using TTL-based freshness checks.

caching ttl resilience

Python

import time
from functools import lru_cache


class CachedService:
    def __init__(self, fetch_func, ttl=5):
        self.fetch_func = fetch_func
        self.ttl = ttl
        self._cache = {}
        self._timestamp = {}

    def get(self, key):
        now = time.time()
        if key in self._cache and now - self…

12 0 Open

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