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"""This is a recursive web crawler. Don't go pointing this at random sites;
it doesn't respect robots.txt and it is pretty brutal about how quickly it
fetches pages.
This is a kind of "producer/consumer" example; the fetch function produces
jobs, and the GreenPool itself is the consumer, farming out work concurrently.
It's easier to write it this way rather than writing a standard consumer loop;
GreenPool handles any exceptions raised and arranges so that there's a set
number of "workers", so you don't have to write that tedious management code
yourself.
"""
from eventlet.green import urllib2
import eventlet
import re
# http://daringfireball.net/2009/11/liberal_regex_for_matching_urls
url_regex = re.compile(r'\b(([\w-]+://?|www[.])[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|/)))')
def fetch(url, outq):
"""Fetch a url and push any urls found into a queue."""
print("fetching", url)
data = ''
with eventlet.Timeout(5, False):
data = urllib2.urlopen(url).read()
for url_match in url_regex.finditer(data):
new_url = url_match.group(0)
outq.put(new_url)
def producer(start_url):
"""Recursively crawl starting from *start_url*. Returns a set of
urls that were found."""
pool = eventlet.GreenPool()
seen = set()
q = eventlet.Queue()
q.put(start_url)
# keep looping if there are new urls, or workers that may produce more urls
while True:
while not q.empty():
url = q.get()
# limit requests to eventlet.net so we don't crash all over the internet
if url not in seen and 'eventlet.net' in url:
seen.add(url)
pool.spawn_n(fetch, url, q)
pool.waitall()
if q.empty():
break
return seen
seen = producer("http://eventlet.net")
print("I saw these urls:")
print("\n".join(seen))
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