[项目实训]Python正则表达式和Re库

正则表达式

定义：正则表达式是用来简洁表达一组字符串的表达式 

例：匹配IP地址的正则表达式

IP地址字符串形式的正则表达式(IP地址分4段，每段0‐255)\d+.\d+.\d+.\d+或
\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}

精确写法 

0‐99:[1‐9]?\d

100‐199:1\d{2}

200‐249:2[0‐4]\d

250‐255:25[0‐5]

(([1‐9]?\d|1\d{2}|2[0‐4]\d|25[0‐5]).){3}([1‐9]？\d|1\d{2}|2[0‐4]\d|25[0‐5]) 

Re库

raw string类型(原生字符串类型)

re库采用raw string类型表示正则表达式，表示为:r'text'

例如:
r'[1‐9]\d{5}'r'\d{3}‐\d{8}|\d{4}‐\d{7}'

raw string是不包含对转义符再次转义的字符串 

实例：淘宝定向爬虫

import requests
import re
import sys

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():
print(sys.getdefaultencoding())
goods = '书包'
depth = 2
start_url = 'http://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
print(len(infoList))
printGoodsList(infoList)

main()