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from threading import Thread
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from urllib.robotparser import RobotFileParser
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from urllib.error import URLError
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from urllib.parse import urlparse
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from ssl import CertificateError
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from random import sample, randrange
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import re
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from datetime import datetime, timedelta
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import asyncio
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import aiohttp
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import async_timeout
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from bs4 import BeautifulSoup, Comment
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# Ugly hack to use this module alone instead of integrating it with Django
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# from django.conf import settings
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# Gets all the direct bookmarks in the html.
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# We want this to avoid following this kind of bookmark
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HARD_LIMIT = 20
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MAX_PER_PAGE = 10
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FOOTER_URL = re.compile(".*footer.*")
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class Settings:
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USER_AGENT = 'Blah'
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settings = Settings()
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startup_time = datetime.now()
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def url_getter(html, current_page, root_url):
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links_list = [] # The final resutl
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soup = BeautifulSoup(html, "html.parser")
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# Get only the body
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body = soup.find('body')
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if not body:
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return links_list
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# remove the body
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if body.footer:
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body.footer.decompose()
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# remove all comments
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comments = soup.findAll(text=lambda text: isinstance(text, Comment))
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for comment in comments:
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comment.extract()
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footers = soup.findAll(id=FOOTER_URL)
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for footer in footers:
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footer.extract()
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# Remove all bookmark links pointing to the current html page.
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links = map(lambda link: link.get("href", ""), body.find_all("a"))
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for link in links:
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if link: #Edge case, if no href found.
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if link.startswith("http"):
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links_list.append(link)
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elif link.startswith('/'): #Internal link, linking to page root url
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links_list.append(root_url + link)
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elif link.startswith("#"):
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continue
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else:
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links_list.append(current_page + "/" + link)
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## uniqifier works with python <= 3.6
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#seen = set()
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#links_list = [x for x in links_list if x not in seen and not seen.add(x)]
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# uniqifier
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# Works only with python >= 3.6
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links_list = list(dict.fromkeys(links_list))
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forbidden_words = ['login', 'agreement', 'mailto']
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links_list = [link for link in links_list if not any(word in link.lower()
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for word in
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forbidden_words)]
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return links_list
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class WebsiteSchedulerMeta(type):
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""" Meta-class for WebsiteScheduler, allowing a singleton class-like
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interface, but spawning one instance per canonical website URL """
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_instances = {}
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_canonicalize = re.compile(r'(https?://)?([^/]+)(/?|$)')
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def canonical_url(cls, url):
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""" Canonicalize a url """
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return cls._canonicalize.search(url).groups()[1]
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def __call__(cls, url, *args, **kwargs):
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canonical = cls.canonical_url(url)
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if canonical not in cls._instances:
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cls._instances[canonical] = \
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super(WebsiteSchedulerMeta, cls) \
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.__call__(canonical, *args, **kwargs)
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return cls._instances[canonical]
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class WebsiteScheduler(metaclass=WebsiteSchedulerMeta):
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""" Schedule the accesses to a website as of robots.txt """
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def __init__(self, name):
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self.name = name
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self.last_crawled = datetime.fromtimestamp(0)
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self.dead = False
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try:
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robots_url = self.urlroot() + 'robots.txt'
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self.robot_parser = RobotFileParser(robots_url)
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self.robot_parser.read() # TODO async?
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except (URLError, CertificateError):
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try:
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robots_url = self.unsafe_urlroot() + 'robots.txt'
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self.robot_parser = RobotFileParser(robots_url)
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self.robot_parser.read()
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except URLError: # Almost surely an offline website.
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self.dead = True
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self.crawl_delay = 0
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except Exception as e:
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print(e)
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raise e
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if not self.robot_parser.default_entry:
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self.dead = True
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if not self.dead:
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delay = self.robot_parser.crawl_delay(settings.USER_AGENT)
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if delay is None:
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req_rate = self.robot_parser.request_rate(settings.USER_AGENT)
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if req_rate is None:
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delay = 5
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else:
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delay = req_rate.requests, req_rate.seconds
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self.crawl_delay = timedelta(seconds=delay)
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def urlroot(self):
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''' Get the root url for this website '''
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return 'https://{}/'.format(self.name)
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def unsafe_urlroot(self):
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return 'http://{}/'.format(self.name)
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def fetch_delay(self):
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''' Get the delay needed before fetching a page is possible '''
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can_fetch_time = self.last_crawled + self.crawl_delay
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if can_fetch_time < datetime.now():
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return timedelta(0)
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return can_fetch_time - datetime.now()
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def can_fetch(self, url):
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''' Check whether this program can fetch a given page '''
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return (not self.dead) and self.robot_parser.can_fetch(settings.USER_AGENT, url)
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def fetching(self):
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''' Tell the scheduler that a page is being fetched now '''
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self.last_crawled = datetime.now()
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class CrawlingThread(Thread):
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""" A separate thread for the crawling task. This is needed to use asyncio,
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since the thread will need its own event loop. """
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def __init__(self):
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super(CrawlingThread, self).__init__()
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def run(self):
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tasks = []
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#tasks.append(async_crawler("http://plus.google.com/+Python"))
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tasks.append(async_crawler('https://python.org/'))
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loop = asyncio.new_event_loop()
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asyncio.set_event_loop(loop)
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loop.run_until_complete(asyncio.wait(tasks))
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loop.close()
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class PageGetter:
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""" Asynchronously get a webpage, abiding by robots.txt """
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def __init__(self, session, url):
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self.url = url
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self.session = session
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async def get(self, ssl=True):
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""" Actually retrieve the webpage """
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scheduler = WebsiteScheduler(self.url)
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if not scheduler.can_fetch(self.url):
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return None
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delay = scheduler.fetch_delay()
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while delay > timedelta(0):
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await asyncio.sleep(delay.total_seconds())
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delay = scheduler.fetch_delay()
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scheduler.fetching()
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async with async_timeout.timeout(10):
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async with self.session.get(self.url, ssl=ssl) as resp:
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try:
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return await resp.text()
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except UnicodeDecodeError:
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return None
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async def async_print(url):
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""" Debug function to follow what's actually happening """
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async with aiohttp.ClientSession() as session:
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html = await PageGetter(session, url).get(ssl=False)
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print('GOT {}HTML for {} at {}'.format(
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'None ' if html is None else '',
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url,
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datetime.now() - startup_time))
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async def async_crawler(url):
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queue = [url]
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crawled = []
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while queue and (len(crawled) < HARD_LIMIT):
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async with aiohttp.ClientSession() as session:
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try:
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url = queue.pop(0)
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except IndexError:
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print("Error queue is empty")
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return crawled
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parsed_url = urlparse(url)
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print("Crawling {}".format(url))
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html = await PageGetter(session, url).get(ssl=False)
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if html:
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new_urls = url_getter(
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html,
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url,
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parsed_url.scheme + "://" + parsed_url.netloc
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)
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crawled += [url]
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if new_urls:
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sampled = sample(
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new_urls,
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randrange(min(MAX_PER_PAGE, len(new_urls)))
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)
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queue += [sample_url for sample_url in sampled if
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sample_url not in queue and sample_url not in
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crawled]
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print(crawled)
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return crawled
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if __name__ == '__main__':
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crawl = CrawlingThread()
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crawl.start()
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crawl.join()
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