Python网络爬虫与信息提取(三)：网络爬虫之实战

Re(正则表达式)库入门

regular expression = regex = RE是一种通用的字符串表达框架,用来简洁表达一组字符串的表达式,也可用来判断某字符串的特征归属

正则表达式的语法

常用操作符

实例

Re库的基本使用

• 正则表达式的表示类型为raw string类型(原生字符串类型),表示为r’text’

• Re库主要功能函数
  

• 功能函数

• re.search(pattern,string,flags=0)

- re.match(pattern,string,flags=0)

因为match为从开始位置开始匹配,使用时要加if进行判别返回结果是否为空,否则会报错

• re.findall(pattern,string,flags=0)
  

• re.split(pattern,string,maxsplit=0,flags=0)

  maxsplit为最大分割数,剩余部分作为最后一个元素输出

• re.finditer(pattern,string,flags=0)

• re.sub(pattern,repl,string,count=0,flags=0)

  repl是用来替换的字符串,count为替换次数

• Re库的另一种等价用法

Re库的函数式用法为一次性操作,还有一种为面向对象用法,可在编译后多次操作

regex = re.compile(pattern,flags=0)

通过compile生成的regex对象才能被叫做正则表达式

Match对象的属性

Match对象的方法

例子

Re库的贪婪匹配和最小匹配Re库默认采取贪婪匹配,即输出匹配最长的子串

实例二:淘宝商品比价定向爬虫(requests-re)

步骤1:提交商品搜索请求,循环获取页面步骤2:对于每个页面,提取商品名称和价格信息步骤3:将信息输出显示

import requestsimport redef getHTMLText(url):    try:        r = requests.get(url, timeout=30)        r.raise_for_status()        r.encoding = r.apparent_encoding        return r.text    except:        return ""def parsePage(ilt, html):    try:        plt = re.findall(r'\"view_price\"\:\"[\d\.]*\"',html)        tlt = re.findall(r'\"raw_title\"\:\".*?\"',html)        for i in range(len(plt)):            price = eval(plt[i].split(':')[1])            title = eval(tlt[i].split(':')[1])            ilt.append([price , title])    except:        print("")def printGoodsList(ilt):    tplt = "{:4}\t{:8}\t{:16}"    print(tplt.format("序号", "价格", "商品名称"))    count = 0    for g in ilt:        count = count + 1        print(tplt.format(count, g[0], g[1]))def main():    goods = '书包'    depth = 3    start_url = 'https://s.taobao.com/search?q=' + goods    infoList = []    for i in range(depth):        try:            url = start_url + '&s=' + str(44*i)            html = getHTMLText(url)            parsePage(infoList, html)        except:            continue    printGoodsList(infoList)main()

实例三:股票数据定向爬虫

步骤1:从东方财富网获取股票列表步骤2:根据股票列表逐个到百度股票获取个股信息步骤3:将结果存储到文件

#CrawBaiduStocksB.pyimport requestsfrom bs4 import BeautifulSoupimport tracebackimport redef getHTMLText(url, code="utf-8"):    try:        r = requests.get(url)        r.raise_for_status()        r.encoding = code        return r.text    except:        return ""def getStockList(lst, stockURL):    html = getHTMLText(stockURL, "GB2312")    soup = BeautifulSoup(html, 'html.parser')     a = soup.find_all('a')    for i in a:        try:            href = i.attrs['href']            lst.append(re.findall(r"[s][hz]\d{6}", href)[0])        except:            continuedef getStockInfo(lst, stockURL, fpath):    count = 0    for stock in lst:        url = stockURL + stock + ".html"        html = getHTMLText(url)        try:            if html=="":                continue            infoDict = {}            soup = BeautifulSoup(html, 'html.parser')            stockInfo = soup.find('div',attrs={'class':'stock-bets'})            name = stockInfo.find_all(attrs={'class':'bets-name'})[0]            infoDict.update({'股票名称': name.text.split()[0]})            keyList = stockInfo.find_all('dt')            valueList = stockInfo.find_all('dd')            for i in range(len(keyList)):                key = keyList[i].text                val = valueList[i].text                infoDict[key] = val            with open(fpath, 'a', encoding='utf-8') as f:                f.write( str(infoDict) + '\n' )                count = count + 1                print("\r当前进度: {:.2f}%".format(count*100/len(lst)),end="")        except:            count = count + 1            print("\r当前进度: {:.2f}%".format(count*100/len(lst)),end="")            continuedef main():    stock_list_url = 'http://quote.eastmoney.com/stocklist.html'    stock_info_url = 'https://gupiao.baidu.com/stock/'    output_file = 'D:/BaiduStockInfo.txt'    slist=[]    getStockList(slist, stock_list_url)    getStockInfo(slist, stock_info_url, output_file)main()