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
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正则表达式的语法
常用操作符1
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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'
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Re库主要功能函数
功能函数-
re.search(pattern,string,flags=0)
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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
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re.findall(pattern,string,flags=0)
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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
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re.finditer(pattern,string,flags=0)
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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
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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
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Re库的match对象
Match对象的属性
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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()
