python实现爬虫

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)