限制/限制GRequests中HTTP请求的速率

Question

我正在用GRequests和lxml在Python
2.7.3中编写一个小脚本，这将允许我从各个网站收集一些可收集的卡价格并进行比较。问题是网站之一限制了请求的数量，如果我超过了它，则会发回HTTP错误429。

有没有一种方法可以限制GRequestes中的请求数量，以使我不超过我指定的每秒请求数量？另外-如果发生HTTP
429，如何让GRequestes在一段时间后重试？

附带说明-它们的极限太低了。大约每15秒8个请求。我多次用浏览器破坏它，只是刷新页面以等待价格变动。

Answer 1

因为我不得不自己解决这个问题，所以要回答我自己的问题，并且关于此问题的信息似乎很少。

这个想法如下。与GRequests一起使用的每个请求对象在创建时都可以将会话对象作为参数。另一方面，会话对象可以安装在发出请求时使用的HTTP适配器。通过创建我们自己的适配器，我们可以拦截请求并对请求进行速率限制，从而找到最适合我们的应用程序的方式。就我而言，我得到了下面的代码。

用于限制的对象：

DEFAULT_BURST_WINDOW = datetime.timedelta(seconds=5)
DEFAULT_WAIT_WINDOW = datetime.timedelta(seconds=15)


class BurstThrottle(object):
    max_hits = None
    hits = None
    burst_window = None
    total_window = None
    timestamp = None

    def __init__(self, max_hits, burst_window, wait_window):
        self.max_hits = max_hits
        self.hits = 0
        self.burst_window = burst_window
        self.total_window = burst_window + wait_window
        self.timestamp = datetime.datetime.min

    def throttle(self):
        now = datetime.datetime.utcnow()
        if now < self.timestamp + self.total_window:
            if (now < self.timestamp + self.burst_window) and (self.hits < self.max_hits):
                self.hits += 1
                return datetime.timedelta(0)
            else:
                return self.timestamp + self.total_window - now
        else:
            self.timestamp = now
            self.hits = 1
            return datetime.timedelta(0)

HTTP适配器：

class MyHttpAdapter(requests.adapters.HTTPAdapter):
    throttle = None

    def __init__(self, pool_connections=requests.adapters.DEFAULT_POOLSIZE,
                 pool_maxsize=requests.adapters.DEFAULT_POOLSIZE, max_retries=requests.adapters.DEFAULT_RETRIES,
                 pool_block=requests.adapters.DEFAULT_POOLBLOCK, burst_window=DEFAULT_BURST_WINDOW,
                 wait_window=DEFAULT_WAIT_WINDOW):
        self.throttle = BurstThrottle(pool_maxsize, burst_window, wait_window)
        super(MyHttpAdapter, self).__init__(pool_connections=pool_connections, pool_maxsize=pool_maxsize,
                                            max_retries=max_retries, pool_block=pool_block)

    def send(self, request, stream=False, timeout=None, verify=True, cert=None, proxies=None):
        request_successful = False
        response = None
        while not request_successful:
            wait_time = self.throttle.throttle()
            while wait_time > datetime.timedelta(0):
                gevent.sleep(wait_time.total_seconds(), ref=True)
                wait_time = self.throttle.throttle()

            response = super(MyHttpAdapter, self).send(request, stream=stream, timeout=timeout,
                                                       verify=verify, cert=cert, proxies=proxies)

            if response.status_code != 429:
                request_successful = True

        return response

设定：

requests_adapter = adapter.MyHttpAdapter(
    pool_connections=__CONCURRENT_LIMIT__,
    pool_maxsize=__CONCURRENT_LIMIT__,
    max_retries=0,
    pool_block=False,
    burst_window=datetime.timedelta(seconds=5),
    wait_window=datetime.timedelta(seconds=20))

requests_session = requests.session()
requests_session.mount('http://', requests_adapter)
requests_session.mount('https://', requests_adapter)

unsent_requests = (grequests.get(url,
                                 hooks={'response': handle_response},
                                 session=requests_session) for url in urls)
grequests.map(unsent_requests, size=__CONCURRENT_LIMIT__)