Re模組正則表示式

概念

• 正則表示式是對字串串操作的⼀一種邏輯公式，就是⽤用事先定義好的⼀一些特定
  字元、及這些特定字元的組合，組成⼀一個“規則字串串”，這個“規則字串串”⽤用
  來表達對字串串的⼀一種過濾邏輯
• 非python獨有，re模組實現
  • re.match
  • re.search
  • re.findall
  • re.sub
  • re.compile
• 正則表示式線上工具：http://tool.oschina.net/regex

Re常用匹配模式

Re模組例項

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

• re.match 嘗試從字串的起始位置匹配一個模式，如果不是起始位置匹配成功的話，match()就返回none

常規匹配

import re
content = 'Hello 123 4567 World_This is a Regex Demo'
print(len(content))
result = re.match('^Hello\s\d\d\d\s\d{4}\s\w{10}.*Demo$', content)
print(result)
print(result.group())#返回匹配結果
print(result.span())#返回匹配結果範圍

泛匹配

import re
content = 'Hello 123 4567 World_This is a Regex Demo'
result = re.match('^Hello.*Demo$', content)
print(result)
print(result.group())
print(result.span())

匹配目標

import re
content = 'Hello 1234567 World_This is a Regex Demo'
result = re.match('^Hello\s(\d+)\sWorld.*Demo$', content)
print(result)
print(result.group(1))#group(1)分離匹配結果，1表示匹配到的第一個括號內的資料，這裡是1234567
print(result.span())

貪婪匹配

import re
content = 'Hello 1234567 World_This is a Regex Demo'
result = re.match('^He.*(\d+).*Demo$', content)#.*會盡可能多的匹配字元
print(result)
print(result.group(1))

非貪婪匹配

import re
content = 'Hello 1234567 World_This is a Regex Demo'
result = re.match('^He.*?(\d+).*Demo$', content)#.*?會盡可能少的匹配字元
print(result)
print(result.group(1))

匹配模式

import re
content = '''Hello 1234567 World_This
is a Regex Demo
'''
result = re.match('^He.*?(\d+).*?Demo$', content, re.S)#re.S匹配任意字元模式
print(result.group(1))

轉義

import re
content = 'price is $5.00'
result = re.match('price is $5.00', content)
print(result)

import re
content = 'price is $5.00'
result = re.match('price is \$5\.00', content)
print(result)

儘量使用泛匹配、使用括號得到匹配目標、儘量使用非貪婪模式、有換行符就用re.S

• re.search

re.search 掃描整個字串並返回第一個成功的匹配

import re
content = 'Extra stings Hello 1234567 World_This is a Regex Demo Extra stings'
result = re.match('Hello.*?(\d+).*?Demo', content)
print(result)

import re
content = 'Extra stings Hello 1234567 World_This is a Regex Demo Extra stings'
result = re.search('Hello.*?(\d+).*?Demo', content)
print(result)
print(result.group(1))

為匹配方便，能用search就不用match

import re

html = '''<div id="songs-list">
    <h2 class="title">經典老歌</h2>
    <p class="introduction">
        經典老歌列表
    </p>
    <ul id="list" class="list-group">
        <li data-view="2">一路上有你</li>
        <li data-view="7">
            <a href="/2.mp3" singer="任賢齊">滄海一聲笑</a>
        </li>
        <li data-view="4" class="active">
            <a href="/3.mp3" singer="齊秦">往事隨風</a>
        </li>
        <li data-view="6"><a href="/4.mp3" singer="beyond">光輝歲月</a></li>
        <li data-view="5"><a href="/5.mp3" singer="陳慧琳">記事本</a></li>
        <li data-view="5">
            <a href="/6.mp3" singer="鄧麗君"><i class="fa fa-user"></i>但願人長久</a>
        </li>
    </ul>
</div>'''
result = re.search('<li.*?active.*?singer="(.*?)">(.*?)</a>', html, re.S)
if result:
    print(result.group(1), result.group(2))
    
result = re.search('<li.*?singer="(.*?)">(.*?)</a>', html, re.S)
if result:
    print(result.group(1), result.group(2))
    
result = re.search('<li.*?singer="(.*?)">(.*?)</a>', html)
if result:
    print(result.group(1), result.group(2))

• re.findall

  搜尋字串，以列表形式返回全部能匹配的子串

import re

html = '''<div id="songs-list">
    <h2 class="title">經典老歌</h2>
    <p class="introduction">
        經典老歌列表
    </p>
    <ul id="list" class="list-group">
        <li data-view="2">一路上有你</li>
        <li data-view="7">
            <a href="/2.mp3" singer="任賢齊">滄海一聲笑</a>
        </li>
        <li data-view="4" class="active">
            <a href="/3.mp3" singer="齊秦">往事隨風</a>
        </li>
        <li data-view="6"><a href="/4.mp3" singer="beyond">光輝歲月</a></li>
        <li data-view="5"><a href="/5.mp3" singer="陳慧琳">記事本</a></li>
        <li data-view="5">
            <a href="/6.mp3" singer="鄧麗君">但願人長久</a>
        </li>
    </ul>
</div>'''
results = re.findall('<li.*?href="(.*?)".*?singer="(.*?)">(.*?)</a>', html, re.S)
print(results)
print(type(results))
for result in results:
    print(result)
    print(result[0], result[1], result[2])
    
results = re.findall('<li.*?>\s*?(<a.*?>)?(\w+)(</a>)?\s*?</li>', html, re.S)
print(results)
for result in results:
    print(result[1])

• re.sub

  替換字串中每一個匹配的子串後返回替換後的字串

  import re
  content = 'Extra stings Hello 1234567 World_This is a Regex Demo Extra stings'
  content = re.sub('\d+', '', content)
  print(content)
  

  import re
  content = 'Extra stings Hello 1234567 World_This is a Regex Demo Extra stings'
  content = re.sub('(\d+)', r'\1 8910', content)
  print(content)
  #Extra stings Hello 1234567 8910 World_This is a Regex Demo Extra stings
  

  import re
  
  html = '''<div id="songs-list">
      <h2 class="title">經典老歌</h2>
      <p class="introduction">
          經典老歌列表
      </p>
      <ul id="list" class="list-group">
          <li data-view="2">一路上有你</li>
          <li data-view="7">
              <a href="/2.mp3" singer="任賢齊">滄海一聲笑</a>
          </li>
          <li data-view="4" class="active">
              <a href="/3.mp3" singer="齊秦">往事隨風</a>
          </li>
          <li data-view="6"><a href="/4.mp3" singer="beyond">光輝歲月</a></li>
          <li data-view="5"><a href="/5.mp3" singer="陳慧琳">記事本</a></li>
          <li data-view="5">
              <a href="/6.mp3" singer="鄧麗君">但願人長久</a>
          </li>
      </ul>
  </div>'''
  html = re.sub('<a.*?>|</a>', '', html)
  print(html)
  results = re.findall('<li.*?>(.*?)</li>', html, re.S)
  print(results)
  for result in results:
      print(result.strip())
  

• re.compile

  將正則字串編譯成正則表示式物件，以便於複用該匹配模式

import re
content = '''Hello 1234567 World_This
is a Regex Demo'''
pattern = re.compile('Hello.*Demo', re.S)
result = re.match(pattern, content)
#result = re.match('Hello.*Demo', content, re.S)
print(result)

綜合例項

• 爬取豆瓣讀書首頁書籍資訊

import requests
import re
content = requests.get('https://book.douban.com/').text
pattern = re.compile('<li.*?title=.*?href="(.*?)".*?title="(.*?)".*?more-meta.*?author">\n(.*?)\n.*?year">\n(.*?)\n.*?</li>', re.S)
results = re.findall(pattern, content)
for result in results:
    url, name, author, year = result
    author = re.sub('\s', '', author)
    year = re.sub('\s', '', year)
    print(url, name, author, year)