Auto Rollback on Error Rate Exceeded in Python

import random
import time


def simulate_requests(total_requests=1000, rollback_threshold=0.2):
    """
    Simulate a service that automatically rolls back when the error rate
    exceeds a threshold within a rolling window.
    """
    window_size = 100
    errors_seen = []
    rolled_back = False

    for req_num in range(1, total_requests + 1):
        # Simulate error with ~10% baseline, but introduce a spike mid-way
        error_rate = 0.10 if req_num < 400 else (0.30 if req_num < 700 else 0.05)
        is_error = random.random() < error_rate
        errors_seen.append(is_error)

        # Keep only the last `window_size` requests
        if len(errors_seen) > window_size:
            errors_seen.pop(0)

        # Check error rate in the current window
        if len(errors_seen) == window_size:
            current_error_rate = sum(errors_seen) / window_size
            if current_error_rate > rollback_threshold and not rolled_back:
                rolled_back = True
                print(f"ROLLBACK triggered at request #{req_num} "
                      f"(window error rate: {current_error_rate:.2%})")
                return  # Stop processing after rollback

        # Simulate processing time
        time.sleep(0)

    print(f"Completed {total_requests} requests without rollback "
          f"(final error rate: {sum(errors_seen) / len(errors_seen):.2%})")


if __name__ == "__main__":
    random.seed(123)
    simulate_requests()