python实现爬虫

时间：2010-08-25 来源：bigluo

爬虫工作的基本原理就是，给定一个初始的url，下载这个url的网页，然后找出网页上所有满足下载要求的链接，然后把这些链接对应的url下载下来，然后再找下载下来的这些网页的url，我们可以用广度优先搜索实现这个算法.

#!/usr/bin/python
import urllib2
import re

def downURL(url,filename):
print url
print filename
try:
fp = urllib2.urlopen(url)
except:
print 'download exception'
return 0
op = open(filename,"wb")
while 1:
s = fp.read()
if not s:
break
op.write(s)

fp.close()
fp.close()
return 1

#downURL('http://www.sohu.com','http.log')

def getURL(url):
try:
fp = urllib2.urlopen(url)
except:
print 'get url exception'
return 0

pattern = re.compile("http://sports.sina.com.cn/[^\>]+.shtml")
while 1:
s = fp.read()
if not s:
break
urls = pattern.findall(s)
fp.close()
return urls

def spider(startURL,times):
urls = []
urls.append(startURL)
i = 0
while 1:
if i > times:
break;
if len(urls)>0:
url = urls.pop(0)
print url,len(urls)
downURL(url,str(i)+'.htm')
i = i + 1
if len(urls)<times:
urllist = getURL(url)
for url in urllist:
if urls.count(url) == 0:
urls.append(url)
else:
break
return 1
spider('http://www.sina.com.cn',10)

几个爬虫的库
http://pypi.python.org/pypi?:action=browse&c=334

一个不错的小库，这个站点也是一个不错的入门级别的站点。例子代码很好。
http://www.example-code.com/python/spider_begin.asp