它以网络上的网址开头（例如：http://python.org），获取与该网址对应的网页，并将该网页上的所有链接解析为链接存储库。接下来，它从刚刚创建的存储库中获取任何url的内容，将此新内容中的链接解析到存储库，并继续对存储库中的所有链接执行此过程，直到停止或获取给定数量的链接为止。 / p>
我怎么能用python和scrapy做到这一点？我能够抓取网页中的所有链接，但如何以递归方式执行它
答案 0 :(得分：1)
几条评论：
下面是一个简单的实现：它没有提取内部链接（只有绝对形成的超链接），也没有任何错误处理（403,404，没有链接，...），而且它非常慢（multiprocessing在这种情况下，模块可以提供很多帮助）。
import BeautifulSoup
import urllib2
import itertools
import random
class Crawler(object):
"""docstring for Crawler"""
def __init__(self):
self.soup = None # Beautiful Soup object
self.current_page = "http://www.python.org/" # Current page's address
self.links = set() # Queue with every links fetched
self.visited_links = set()
self.counter = 0 # Simple counter for debug purpose
def open(self):
# Open url
print self.counter , ":", self.current_page
res = urllib2.urlopen(self.current_page)
html_code = res.read()
self.visited_links.add(self.current_page)
# Fetch every links
self.soup = BeautifulSoup.BeautifulSoup(html_code)
page_links = []
try :
page_links = itertools.ifilter( # Only deal with absolute links
lambda href: 'http://' in href,
( a.get('href') for a in self.soup.findAll('a') ) )
except Exception: # Magnificent exception handling
pass
# Update links
self.links = self.links.union( set(page_links) )
# Choose a random url from non-visited set
self.current_page = random.sample( self.links.difference(self.visited_links),1)[0]
self.counter+=1
def run(self):
# Crawl 3 webpages (or stop if all url has been fetched)
while len(self.visited_links) < 3 or (self.visited_links == self.links):
self.open()
for link in self.links:
print link
if __name__ == '__main__':
C = Crawler()
C.run()
输出：
In [48]: run BFScrawler.py
0 : http://www.python.org/
1 : http://twistedmatrix.com/trac/
2 : http://www.flowroute.com/
http://www.egenix.com/files/python/mxODBC.html
http://wiki.python.org/moin/PyQt
http://wiki.python.org/moin/DatabaseProgramming/
http://wiki.python.org/moin/CgiScripts
http://wiki.python.org/moin/WebProgramming
http://trac.edgewall.org/
http://www.facebook.com/flowroute
http://www.flowroute.com/
http://www.opensource.org/licenses/mit-license.php
http://roundup.sourceforge.net/
http://www.zope.org/
http://www.linkedin.com/company/flowroute
http://wiki.python.org/moin/TkInter
http://pypi.python.org/pypi
http://pycon.org/#calendar
http://dyn.com/
http://www.google.com/calendar/ical/j7gov1cmnqr9tvg14k621j7t5c%40group.calendar.
google.com/public/basic.ics
http://www.pygame.org/news.html
http://www.turbogears.org/
http://www.openbookproject.net/pybiblio/
http://wiki.python.org/moin/IntegratedDevelopmentEnvironments
http://support.flowroute.com/forums
http://www.pentangle.net/python/handbook/
http://dreamhost.com/?q=twisted
http://www.vrplumber.com/py3d.py
http://sourceforge.net/projects/mysql-python
http://wiki.python.org/moin/GuiProgramming
http://software-carpentry.org/
http://www.google.com/calendar/ical/3haig2m9msslkpf2tn1h56nn9g%40group.calendar.
google.com/public/basic.ics
http://wiki.python.org/moin/WxPython
http://wiki.python.org/moin/PythonXml
http://www.pytennessee.org/
http://labs.twistedmatrix.com/
http://www.found.no/
http://www.prnewswire.com/news-releases/voip-innovator-flowroute-relocates-to-se
attle-190011751.html
http://www.timparkin.co.uk/
http://docs.python.org/howto/sockets.html
http://blog.python.org/
http://docs.python.org/devguide/
http://www.djangoproject.com/
http://buildbot.net/trac
http://docs.python.org/3/
http://www.prnewswire.com/news-releases/flowroute-joins-voxbones-inum-network-fo
r-global-voip-calling-197319371.html
http://www.psfmember.org
http://docs.python.org/2/
http://wiki.python.org/moin/Languages
http://sip-trunking.tmcnet.com/topics/enterprise-voip/articles/341902-grandstrea
m-ip-voice-solutions-receive-flowroute-certification.htm
http://www.twitter.com/flowroute
http://wiki.python.org/moin/NumericAndScientific
http://www.google.com/calendar/ical/b6v58qvojllt0i6ql654r1vh00%40group.calendar.
google.com/public/basic.ics
http://freecode.com/projects/pykyra
http://www.xs4all.com/
http://blog.flowroute.com
http://wiki.python.org/moin/PyGtk
http://twistedmatrix.com/trac/
http://wiki.python.org/moin/
http://wiki.python.org/moin/Python2orPython3
http://stackoverflow.com/questions/tagged/twisted
http://www.pycon.org/
答案 1 :(得分：0)
以下是从网页递归写入剪贴簿链接的主要抓取方法。此方法将抓取URL并将所有已爬网的URL放入缓冲区。现在，多个线程将等待从此全局缓冲区弹出URL，并再次调用此爬网方法。
def crawl(self,urlObj):
'''Main function to crawl URL's '''
try:
if ((urlObj.valid) and (urlObj.url not in CRAWLED_URLS.keys())):
rsp = urlcon.urlopen(urlObj.url,timeout=2)
hCode = rsp.read()
soup = BeautifulSoup(hCode)
links = self.scrap(soup)
boolStatus = self.checkmax()
if boolStatus:
CRAWLED_URLS.setdefault(urlObj.url,"True")
else:
return
for eachLink in links:
if eachLink not in VISITED_URLS:
parsedURL = urlparse(eachLink)
if parsedURL.scheme and "javascript" in parsedURL.scheme:
#print("***************Javascript found in scheme " + str(eachLink) + "**************")
continue
'''Handle internal URLs '''
try:
if not parsedURL.scheme and not parsedURL.netloc:
#print("No scheme and host found for " + str(eachLink))
newURL = urlunparse(parsedURL._replace(**{"scheme":urlObj.scheme,"netloc":urlObj.netloc}))
eachLink = newURL
elif not parsedURL.scheme :
#print("Scheme not found for " + str(eachLink))
newURL = urlunparse(parsedURL._replace(**{"scheme":urlObj.scheme}))
eachLink = newURL
if eachLink not in VISITED_URLS: #Check again for internal URL's
#print(" Found child link " + eachLink)
CRAWL_BUFFER.append(eachLink)
with self._lock:
self.count += 1
#print(" Count is =================> " + str(self.count))
boolStatus = self.checkmax()
if boolStatus:
VISITED_URLS.setdefault(eachLink, "True")
else:
return
except TypeError:
print("Type error occured ")
else:
print("URL already present in visited " + str(urlObj.url))
except socket.timeout as e:
print("**************** Socket timeout occured*******************" )
except URLError as e:
if isinstance(e.reason, ConnectionRefusedError):
print("**************** Conn refused error occured*******************")
elif isinstance(e.reason, socket.timeout):
print("**************** Socket timed out error occured***************" )
elif isinstance(e.reason, OSError):
print("**************** OS error occured*************")
elif isinstance(e,HTTPError):
print("**************** HTTP Error occured*************")
else:
print("**************** URL Error occured***************")
except Exception as e:
print("Unknown exception occured while fetching HTML code" + str(e))
traceback.print_exc()