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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:
   …

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System design patterns easy

How to Build an Append-Only Event Store in Python

Implement a simple append-only event store class that stores events in a list and supports retrieval by index range.

event-sourcing append-only event-store

Python

class EventStore:
    def __init__(self):
        self._events = []

    def append(self, event):
        """Append an event to the store."""
        self._events.append(event)

    def get_events(self, start=0, end=None):
        """Return events from start index to end (exclusive)."""
        return self._events[sta…

14 0 Open

System design patterns easy

Round Robin Load Balancer in Python

This code simulates round robin load balancing by distributing a list of requests evenly across a list of servers.

load-balancing round-robin system-design

Python

def round_robin_servers(requests: list[str], servers: list[str]) -> dict[str, list[str]]:
    assignments = {server: [] for server in servers}
    for idx, request in enumerate(requests):
        server = servers[idx % len(servers)]
        assignments[server].append(request)
    return assignments


if __name__ == "_…

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