此系列笔记来源于
中国大学MOOC-北京理工大学-嵩天老师的Python系列课程

7. 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1

• 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
    
• Re库的match对象

  

  Match对象的属性

• 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

  

  最小匹配操作符

8.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 requests
import re

def 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()

9.实例三:股票数据定向爬虫(requests-bs

4-re)
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.py
import requests
from bs4 import BeautifulSoup
import traceback
import re

def 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:
            continue

def 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="")
            continue

def 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()