一个简单的搜索引擎 该搜索引擎具有以下功能：通过一个种子链接不断爬取网页，可以指定爬取网页的层数，以此来控制搜索的规模。搜索和关键 字相关的网页的url,并对搜索来的url进行相关性排名，最终返回相关性最高的网页url。
def compute_ranks(graph):
d=0.8 # damping factor
numloops=10
ranks={}
npages=len(graph)
for page in graph:
ranks[page]=1.0/npages
for i in range(0,numloops):
newranks={}
for page in graph:
newranks=(1-d)/npages
for node in graph:
if page in graph[node]:
newrank=newrank+d*(ranks[node])
newranks[page]=newrank
ranks=newranks
return ranks
def get_page(url):
try:
import urllib
return urllib.urlopen(url).read()
except:
return ''
def get_next_target(page):
start_link=page.find(' end_quote=page.find('"',start_quote+1)
url=page[start_quote+1:end_quote]
return url,end_quote
def union(p,q):
for e in q:
if e not in p:
p.append(e):
def get_all_links(page):
links=[]
while True:
url,endpos=get_next_target(page)
if url:
links.append(url)
page=page[endpos:]
else:
break
return links
def add_to_index(index,keyword,url):
if keyword in index:
index[keyword].append(url)
else:
index[keyword]=[url]
def lookup(index,keyword):
if keyword in index:
return index[keyword]
else:
return NOne
def add_page_to_index(index,url,content):
words=content.split()
for word in words:
add_to_index(index,word,url)
def crawl_web(seed,max_depth):
tocrawl=[seed]
crawled=[]
index={}
next_depth=[]
graph={}
depth=0
while tocrawl and depth<=max_depth:
page=tocrawl.pop()
if page not in crawled:
content=get_page(page)
add_page_to_index(index,page,content)
outlinks=get_all_links(content)
graph[page]=outlinks
union(tocrawl,outlinks)
crawled.append(page)
if not tocrawl:
tocrawl,next_depth=next_depth,[]
depth=depth+1
return index,graph
def lucky_search(index,ranks,keyword):
pages=lookup(index,keyword)
if not pages:
return None
best_page=pages[]
for condidate in pages:
if ranks[condidate]>ranks[best_page]:
best_page=condidate
return best_page
index,graph=crawl_web('http://udacity.com/cs101x/urank/index.html',3)
ranks=compute_ranks(graph)
print lucky_search(index,ranks,'Hummus')