Python 爬虫笔记（由站内到站外爬虫）

#! /usr/bin/env python#coding=utf-8import urllib2from    bs4 import  BeautifulSoupimport  reimport datetimeimport randompages=set()random.seed(datetime.datetime.now())#Retrieves a list of all Internal links found on a pagedef getInternalLinks(bsObj, includeUrl):                internalLinks   =   []                #Finds  all links   that    begin   with    a   "/"                for link    in  bsObj.findAll("a",  href=re.compile("^(/|.*"+includeUrl+")")):                                if  link.attrs['href']  is  not None:                                                if  link.attrs['href']  not in  internalLinks:                                                                internalLinks.append(link.attrs['href'])                return  internalLinks#Retrieves a list of all external links found on a pagedef getExternalLinks(bsObj, excludeUrl):                externalLinks   =   []                #Finds  all links   that    start   with    "http"  or  "www"   that    do                #not    contain the current URL                for link    in  bsObj.findAll("a",                                                              href=re.compile("^(http|www)((?!"+excludeUrl+").)*$")):                                if  link.attrs['href']  is  not None:                                                if  link.attrs['href']  not in  externalLinks:                                                                externalLinks.append(link.attrs['href'])                return  externalLinksdef splitAddress(address):                addressParts    =   address.replace("http://",  "").split("/")                return  addressPartsdef getRandomExternalLink(startingPage):                html=   urllib2.urlopen(startingPage)                bsObj   =   BeautifulSoup(html)                externalLinks   =   getExternalLinks(bsObj, splitAddress(startingPage)[0])                if  len(externalLinks)  ==  0:                                internalLinks   =   getInternalLinks(startingPage)                                return  internalLinks[random.randint(0, len(internalLinks)-1)]                else:                                return  externalLinks[random.randint(0, len(externalLinks)-1)]def followExternalOnly(startingSite):                externalLink=getRandomExternalLink("http://oreilly.com")                print("Random   external    link    is: "+externalLink)                followExternalOnly(externalLink)followExternalOnly("http://oreilly.com")