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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 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

System design patterns easy

How to Take Periodic Snapshots of Aggregate State in Python

Build a Python class that accumulates values and periodically captures immutable snapshots of total, count, and average for later analysis.

aggregation snapshots state-management

Python

import time
import random
from collections import defaultdict


class SnapshotAggregator:
    def __init__(self):
        self.total = 0
        self.count = 0
        self.history = []

    def add(self, value):
        self.total += value
        self.count += 1

    def snapshot(self):
        avg = self.total / se…

13 0 Open

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