Python 爬虫入门课作业3－爬虫基础

课程作业

• 选择第二次课程作业中选中的网址
• 爬取该页面中的所有可以爬取的元素，至少要求爬取文章主体内容
• 可以尝试用lxml爬取

作业网址

http://www.jianshu.com/p/e0bd6bfad10b

网页爬取

分别用Beautiful Soup和lxml做了爬取：

• 主页面所有链接，写到 _all_links.txt文件
• 分别抓取各链接，获取文章主体内容和title, 并保存主体内容到以title命名
  的文件
• 对于无title或无主体内容的链接，将url写到Title_Is_None.txt文件中

最后的输出图：

输出

框架结构：

• spidercomm.py: 定义一些公用函数，如写文件，下载页面等，这些函数独立于实际使用的爬取方式

• spiderbs4.py: 定义用BeautifulSoup实现需要的一些函数，如爬取链接，爬取页面内容

• spiderlxml.py: 定义用lxml实现需要的一些函数,如爬取链接，爬取页面内容

• bs4.py: 用BeautifulSoup实现的爬取客户端

• lxml.py: 用lxml实现的爬取客户端

文件夹结果图：

图片.png

BeautifulSoup 实现

BeautifulSoup实现代码

1 导入 spidercomm 和 BeautifulSoup 模块

# -*- coding: utf-8 -*-
import spidercomm as common
from bs4 import BeautifulSoup

2 使用BeautifulSoup 找到所有tag a,spidercomm 模块的爬取所有链接的方法会用到其返回值。

# get all tags a from a single url
def a_links(url_seed,attrs={}):
    html = common.download(url_seed)
    soup = BeautifulSoup(html,'html.parser')
    alinks= soup.find_all('a',attrs)
    return alinks

3 使用BeautifulSoup 爬取某个url的页面，主要关注title和文章主体。

def crawled_page(crawled_url):
        html = common.download(crawled_url)
        soup = BeautifulSoup(html,'html.parser')
        title = soup.find('h1',{'class':'title'})
        if title== None:
            return "Title_Is_None",crawled_url
        content = soup.find('div',{'class':'show-content'})
        if content == None:
            return title.text, "Content_Is_None"
        return title.text,content.text

4 判断是否分页

def isMultiPaged(url):    
    html_page1 = common.download(url % 1)
    soup = BeautifulSoup(html_page1,'html.parser')
    body1 = soup.find('body')   
    body1.script.decompose()
       
    html_page2 = common.download(url % 2)
    if html_page2 == None:
        return False
    soup = BeautifulSoup(html_page2,"html.parser")
    body2 = soup.find('body')
    #print [x.extract() for x in body2.findAll('script') ]
    body2.script.decompose()
    if str(body1) == str(body2):
        return False
    else:
        return True

5 获取所有分页数

def getNumberOfPages(url):
    count = 1
    flag = True
    if (isMultiPaged(url)):
        while flag:
            url= url % count
            # print "url: %s" % url
            count += 1
            html = common.download(url)
            if html==None:
                break        
    return count

BeautifulSoup客户端代码

1 导入spidercomm 和 spiderbs4 模块

# -*- coding: utf-8 -*-
import os
import spiderbs4 as bs4
import spidercomm as common

2 设置所需的变量，创建输出结果路径

# set up             
url_root = 'http://www.jianshu.com/'
url_seed = 'http://www.jianshu.com/p/e0bd6bfad10b?page=%d'
spider_path='spider_res/bs4/'
if os.path.exists(spider_path) == False:
    os.makedirs(spider_path)

3 调用spidercomm的getNumberOfPages方法，判断要爬取的页面是否分页

# get total number of pages
print "url %s has multiple pages? %r" % (url_seed,bs4.isMultiPaged(url_seed))
page_count = bs4.getNumberOfPages(url_seed)
print "page_count is %s" % page_count

4 调用spidercomm的to_be_crawled_links方法，对所要爬取的页面获取所有链接，如果有分页，则分别获取各页并归并获取的链接，并最终将所有链接写入_all_links.txt文件

# get all links to be crawled and write to file    
links_to_be_crawled=set()
for count in range(page_count):
    links = common.to_be_crawled_links(bs4.a_links(url_seed % count),count,url_root,url_seed)
    print "Total number of all links is %d" % len(links)
    links_to_be_crawled = links_to_be_crawled | links
with open(spider_path+"_all_links.txt",'w+') as file:
    file.write("\n".join(unicode(link).encode('utf-8',errors='ignore') for link in links_to_be_crawled))

5 循环所获取的链接列表，爬取每个链接的页面title和页面文章内容，分别写入以title命名的文件中，如无title，则写入Title_Is_None.txt文件中。

# capture desired contents from crawled_urls
if len(links_to_be_crawled) >= 1:
    for link in links_to_be_crawled:           
      title,content=bs4.crawled_page(link) 
      # print "title is %s" % title                
      file_name = spider_path + title +'.txt'
      common.writePage(file_name,content)

lxml 实现

lxml 实现代码

1 导入lxml模块

# -*- coding: utf-8 -*-
import spidercomm as common
import urlparse
from lxml import etree

2 使用lxml找到所有tag a,spidercomm 模块的爬取所有链接的方法会用到其返回值。

# get all tags a from a single url
def a_links(url_seed,attrs={}):
    html = common.download(url_seed)
    tree = etree.HTML(html)
    alinks= tree.xpath("//a")
    return alinks

3 调用spidercomm的getNumberOfPages方法，判断要爬取的页面是否分页

def crawled_page(crawled_url):
        html = common.download(crawled_url)
        tree = etree.HTML(html)
        title= tree.xpath("/html/body/div[1]/div[1]/div[1]/h1")
        if title == None or len(title) == 0:
            return "Title_Is_None",crawled_url
        contents = tree.xpath("/html/body/div[1]/div[1]/div[1]/div[2]/*")
        if contents == None or len(contents) ==0:
            return title.text, "Content_Is_None"
        content = ''
        for x in contents:
            if (x.text != None):
                content = content + x.xpath('string()')
        return title[0].text,content

4 判断是否分页

def isMultiPaged(url):    
    html_page1 = common.download(url % 1)
    tree = etree.HTML(html_page1)    
    xp1 = tree.xpath("/html/body/div[1]/div[1]/div[1]/div[2]/*")
    xp1 = ",".join(x.text for x in xp1)
    html_page2 = common.download(url % 2)
    if html_page2 == None:
        return False
    tree = etree.HTML(html_page2)    
    xp2 = tree.xpath("/html/body/div[1]/div[1]/div[1]/div[2]/*")
    xp2 = ",".join(x.text for x in xp2)
    if xp1 == xp2:
        return False
    else:
        return True

5 获取所有分页数

def getNumberOfPages(url):
    count = 1
    flag = True
    if (isMultiPaged(url)):
        while flag:
            url= url % count
            print "url: %s" % url
            count += 1
            html = common.download(url)
            if html==None:
                break        
    return count   

lxml 客户端代码

同前面的bs4客户端，只是导入的是spiderlxml模块及调用。

公用方法代码

1 导入所需模块

# -*- coding: utf-8 -*-
import urllib2
import time
import urlparse

2 下载页面

def download(url,retry=2):
   # print "downloading %s" % url
    header = {
            'User-Agent':'Mozilla/5.0'
            }
    try:
        req = urllib2.Request(url,headers=header)
        html = urllib2.urlopen(req).read()
    except urllib2.HTTPError as e:
            print "download error: %s" % e.reason
            html = None
            if retry >0:
                print e.code
                if hasattr(e,'code') and 500 <= e.code < 600:
                    print e.code
                    return download(url,retry-1)
                    time.sleep(1)
    return html

3 将爬取内容写入文件

def writePage(filename,content):
    content = unicode(content).encode('utf-8',errors='ignore')+"\n"
    if ('Title_Is_None.txt' in filename):
        with open(filename,'a') as file:
            file.write(content)
    else:
        with open(filename,'wb+') as file:
            file.write(content)

4 获取单一url的所有外链接

# get urls to be crawled
#:param alinks: list of tag 'a' href, dependent on implementation eg. bs4,lxml
def to_be_crawled_link(alinks,url_seed,url_root):
    links_to_be_crawled=set()
    if len(alinks)==0:
        return links_to_be_crawled
    print "len of alinks is %d" % len(alinks)
    for link in alinks:
        link = link.get('href')            
        if link != None and 'javascript:' not in link:
            if link not in links_to_be_crawled:
                realUrl = urlparse.urljoin(url_root,link)
                links_to_be_crawled.add(realUrl)
    return links_to_be_crawled

5 获取指定分页的所有外连接

def to_be_crawled_links(alinks,count,url_root,url_seed):
    url = url_seed % count
    links = to_be_crawled_link(alinks,url_root,url)#,{'class':'title'})
    links.add(url)
    return links

结语：

实现的还很粗糙，抓取的内容也很简单，希望和大家一起讨论，并进一步完善框架。

两种实现爬取下来的页面内容似乎差不多，格式有些差别，bs4的要好一些，可能是自己代码没处理好，需要再研究下，以后要完善的地方还好多，作业先提交吧。