我正在用python 2.7.3编写一个小脚本,其中包含grequests和lxml,它允许我从各种网站收集一些可收集的卡片价格,并对它们进行比较。问题是其中一个网站限制了请求的数量,如果超过了这个数量,就会返回HTTP错误429。
是否有一种方法可以添加限制grequest中的请求数,以使我不超过每秒指定的请求数?另外-如果发生HTTP 429,如何在一段时间后使grequestes重试?
旁注——他们的限额低得离谱。大约每15秒有8个请求。我多次使用浏览器破坏它,只是刷新等待价格变化的页面。
您是否使用grequest在他们的站点注册多个URL?如果是这样,最好同步请求他们的站点,这样您就可以轻松地控制重试。
我同意@dm03514-你不需要grequest。我最近读到一个算法,它可以针对这类问题进行优化。
我试图同时访问同一站点的多个URL,因为我希望能够同时监控多张ATR卡的价格。
@这听起来很有趣。您介意分享一下同步方法吗?
我要自己回答我自己的问题,因为我必须自己解决这个问题,而且这方面的信息似乎很少。
想法如下。与grequest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HTTP适配器,在发出请求时使用这些适配器。通过创建我们自己的适配器,我们可以截获请求,并以最适合我们应用程序的方式对请求进行速率限制。在我的例子中,我最后得到了下面的代码。
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
设置:
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__)
请看一下自动请求限制:https://pypi.python.org/pypi/requeststhrottler/0.2.2
您可以在每个请求之间设置固定的延迟量,也可以在固定的秒数内设置发送的请求数(基本上相同):
import requests
from requests_throttler import BaseThrottler
request = requests.Request(method='GET', url='http://www.google.com')
reqs = [request for i in range(0, 5)] # An example list of requests
with BaseThrottler(name='base-throttler', delay=1.5) as bt:
throttled_requests = bt.multi_submit(reqs)
其中函数multi_submit返回ThrottledRequest的列表(见末尾的doc:link)。
然后您可以访问响应:
for tr in throttled_requests:
print tr.response
或者,您可以通过指定在固定时间内发送的一个或多个请求(例如,每60秒发送15个请求)来实现这一点:
import requests
from requests_throttler import BaseThrottler
request = requests.Request(method='GET', url='http://www.google.com')
reqs = [request for i in range(0, 5)] # An example list of requests
with BaseThrottler(name='base-throttler', reqs_over_time=(15, 60)) as bt:
throttled_requests = bt.multi_submit(reqs)
两种解决方案都可以在不使用with语句的情况下实现:
import requests
from requests_throttler import BaseThrottler
request = requests.Request(method='GET', url='http://www.google.com')
reqs = [request for i in range(0, 5)] # An example list of requests
bt = BaseThrottler(name='base-throttler', delay=1.5)
bt.start()
throttled_requests = bt.multi_submit(reqs)
bt.shutdown()
有关详细信息,请访问:http://pythonhosted.org/requeststhrottler/index.html
它能和grequests一起工作吗?
我也有类似的问题。这是我的解决方案。在你的情况下,我会:
def worker():
with rate_limit('slow.domain.com', 2):
response = requests.get('https://slow.domain.com/path')
text = response.text
# Use `text`
假设你有多个域名,我会设置一个字典映射(domain, delay),这样你就不会达到你的速率限制。
此代码假定您将使用gevent和monkey补丁。
from contextlib import contextmanager
from gevent.event import Event
from gevent.queue import Queue
from time import time
def rate_limit(resource, delay, _queues={}):
"""Delay use of `resource` until after `delay` seconds have passed.
Example usage:
def worker():
with rate_limit('foo.bar.com', 1):
response = requests.get('https://foo.bar.com/path')
text = response.text
# use `text`
This will serialize and delay requests from multiple workers for resource
'foo.bar.com' by 1 second.
"""
if resource not in _queues:
queue = Queue()
gevent.spawn(_watch, queue)
_queues[resource] = queue
return _resource_manager(_queues[resource], delay)
def _watch(queue):
"Watch `queue` and wake event listeners after delay."
last = 0
while True:
event, delay = queue.get()
now = time()
if (now - last) < delay:
gevent.sleep(delay - (now - last))
event.set() # Wake worker but keep control.
event.clear()
event.wait() # Yield control until woken.
last = time()
@contextmanager
def _resource_manager(queue, delay):
"`with` statement support for `rate_limit`."
event = Event()
queue.put((event, delay))
event.wait() # Wait for queue watcher to wake us.
yield
event.set() # Wake queue watcher.
看起来没有任何简单的机制来处理请求或grequests代码中的这个内置项。唯一的钩子似乎是周围的反应。
这里有一个超级黑客的工作,至少证明了这是可能的-我修改了grequest,以保留发出请求的时间列表,并休眠异步请求的创建,直到每秒请求数低于最大值。
class AsyncRequest(object):
def __init__(self, method, url, **kwargs):
print self,'init'
waiting=True
while waiting:
if len([x for x in q if x > time.time()-15]) < 8:
q.append(time.time())
waiting=False
else:
print self,'snoozing'
gevent.sleep(1)
您可以使用grequests.imap()以交互方式观看
import time
import rg
urls = [
'http://www.heroku.com',
'http://python-tablib.org',
'http://httpbin.org',
'http://python-requests.org',
'http://kennethreitz.com',
'http://www.cnn.com',
]
def print_url(r, *args, **kwargs):
print(r.url),time.time()
hook_dict=dict(response=print_url)
rs = (rg.get(u, hooks=hook_dict) for u in urls)
for r in rg.imap(rs):
print r
我希望有一个更优雅的解决方案,但到目前为止我找不到。在会话和适配器中四处查看。也许游泳池管理员可以增加?
此外,我不会将此代码投入生产中,'q'列表永远不会被修剪,最终会变得相当大。另外,我不知道它是否真的像广告上说的那样工作。当我查看控制台输出时,它看起来就是这样。
呃。只要看看这段代码,我就知道是凌晨3点。该睡觉了。