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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 easy

How to Mock a Metrics Decorator in Python with unittest.mock

This code demonstrates a timing decorator that wraps a function to measure execution time and prints the duration, with a unit test using unittest.mock to patch the print function and assert it was called.

decorators unittest.mock metrics

Python

import time
from functools import wraps
from unittest.mock import patch

def add_metrics(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        elapsed = time.perf_counter() - start
        print(f"{func.__name__} took {elapsed:.6f}s…

15 0 Open

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