Rate Limiting with a Simple Python RateLimiter Class

import time

class RateLimiter:
    def __init__(self, max_calls, period_seconds):
        self.max_calls = max_calls
        self.period_seconds = period_seconds
        self.calls = []

    def is_allowed(self):
        now = time.time()
        while self.calls and now - self.calls[0] >= self.period_seconds:
            self.calls.pop(0)
        if len(self.calls) < self.max_calls:
            self.calls.append(now)
            return True
        return False

    def time_until_next_slot(self):
        if not self.calls or len(self.calls) < self.max_calls:
            return 0.0
        return self.period_seconds - (time.time() - self.calls[0])


def validate_positive_int(value):
    try:
        num = int(value)
    except (ValueError, TypeError):
        return False
    return num > 0


if __name__ == "__main__":
    limiter = RateLimiter(max_calls=3, period_seconds=5)

    for attempt in range(1, 6):
        allowed = limiter.is_allowed()
        print(f"Attempt {attempt}: allowed={allowed}")
        if not allowed:
            wait = limiter.time_until_next_slot()
            print(f"  -> Wait {wait:.2f} seconds before next try")
        time.sleep(0.5)