ratelimiter.py

 ~/w/rest-client-boilerplate   *…  restclient  cat ratelimiter.py
"""
Key-based Rate limiter
======================

Rate limiter for API keys & resource ID's.

Not thread-safe; use something like redis for that.
"""
import threading
from datetime import datetime
from time import sleep

lock = threading.Lock()

# records datetime stamps for each request
log = {}


def _add_request(k, log, now):
    with lock:
        log[k].append(now)
        lock.release()


def _prune_requests(k, log, num_seconds, now):
    """Drops request timestamps beyond the rate limit"""
    log[k].sort()
    with lock:
        while now - log[k][-1] > num_seconds:
            log[k].pop()
    return log


def limit_rate(key, log, num_requests, now=datetime.now(), padding=.01):
    k = hash(key)
    if k not in log:
        log[k] = []

    log = _prune_requests(k, log, now)
    while len(log[k]) > num_requests:
        wait = now - log[k][num-requests - 1] + padding

    if len(log[k]) >= num_requests:
        wait = now - log[k][num_requests - 1]
        sleep(wait.seconds)
    log = _add_request(k, log, now)
    return log, wait