Exponential rate limiter with a single variable

ewma.py

#!/usr/bin/env python3
"""Implementation of exponential rate limiter from <https://dotat.at/@/2024-09-02-ewma.html>,
but using a single variable `next-time` to store the state."""
import time
import math


class RateLimiter:
    def __init__(self, window, limit):
        self.next_time = 0.0
        self.window = window
        self.limit = limit

    def rate_at(self, t):
        return self.limit * math.exp((self.next_time - t) / self.window)

    def can_send_at(self, t):
        return t >= self.next_time

    def can_send(self):
        return can_send_at(time.time())

    def send_at(self, t):
        self.next_time = t + self.window * math.log(
            (math.exp((self.next_time - t) / self.window) + 1 / self.limit)
        )

    def send(self):
        self.send_at(time.time())


def main():
    rate_limiter = RateLimiter(window=60, limit=30)
    while True:
        now = time.time()
        if now < rate_limiter.next_time:
            print("sleeping for", rate_limiter.next_time - now)
            time.sleep(rate_limiter.next_time - now)
        rate_limiter.send()
        print(".")


main()