re.match()

re.match 尝试从字符串的起始位置匹配一个模式，如果匹配失败，match()返回none

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

最常规的匹配

import re

content = 'Hello 11223 44445 World_This is Regex Demo'
result = re.match('^Hello\s\d\d\d\d\d\s\d{5}\s\w{10}.*Demo$', content)
print(result)
print(result.group())
print(result.span())

<_sre.SRE_Match object; span=(0, 42), match='Hello 11223 44445 World_This is Regex Demo'>
Hello 11223 44445 World_This is Regex Demo
(0, 42)

泛匹配

import re

content = 'Hello 11223 44445 World_This is Regex Demo'
result = re.match('^Hello.*Demo$', content)
print(result)
print(result.group())
print(result.span())

<_sre.SRE_Match object; span=(0, 42), match='Hello 11223 44445 World_This is Regex Demo'>
Hello 11223 44445 World_This is Regex Demo
(0, 42)

匹配目标

import re

content = 'Hello 11223 44445 World_This is Regex Demo'
result = re.match('^Hello\s(\d+).*Demo$', content)
print(result)
print(result.group(1))
print(result.span())

<_sre.SRE_Match object; span=(0, 42), match='Hello 11223 44445 World_This is Regex Demo'>
11223
(0, 42)

贪婪匹配

.* 会匹配尽可能多的字符

import re

content = 'Hello 11223 44445 World_This is Regex Demo'
result = re.match('^Hello.*(\d+).*Demo$', content)
print(result)
print(result.group(1))
print(result.span())

<_sre.SRE_Match object; span=(0, 42), match='Hello 11223 44445 World_This is Regex Demo'>
5
(0, 42)

非贪婪匹配

.*? 匹配尽可能少的字符
这里，它匹配到第一个数字就停止了
这样就达到我们想取出第一串数字的目的了

import re

content = 'Hello 11223 44445 World_This is Regex Demo'
result = re.match('^Hello.*?(\d+).*Demo$', content)
print(result)
print(result.group(1))
print(result.span())

<_sre.SRE_Match object; span=(0, 42), match='Hello 11223 44445 World_This is Regex Demo'>
11223
(0, 42)

匹配模式

import re

content = '''Hello 11223 44445 World_This 
is Regex Demo
'''
result = re.match('^Hel.*?(\d+).*?Demo$', content, re.S)
print(result)
print(result.group(1))

<_sre.SRE_Match object; span=(0, 43), match='Hello 11223 44445 World_This \nis Regex Demo'>
11223

我们添加re.S是为了给.的匹配模式扩展到整个字符串，包括\n换行符

转义

import re

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

<_sre.SRE_Match object; span=(0, 14), match='price is $5.00'>

可以使用反斜杠进行转义

小结：尽量使用泛匹配，使用括号得到匹配目标，尽量使用非贪婪模式，有换行符要用re.S

---

re.search()

re.search 扫描整个字符串并返回第一个成功匹配的字符

import re

content = 'hei, stt Hello 11223 World_This is Regex Demo'
result = re.search('Hello.*?(\d+).*Demo', content)
print(result)
print(result.group(1))
print(result.span())

<_sre.SRE_Match object; span=(9, 51), match='Hello 11223 44445 World_This is Regex Demo'>
11223
(9, 51)

小结：因为match会限制字符串头部，所以能用search就不用match

---

re.findall()

re.findall 扫描整个字符串并返回所有匹配的字符

import re

content = '''
<div class="info">
  <div class="more-meta">
    <h4 class="title">
      邻人之妻
    </h4>
    <p>
      <span class="author">
        [美] 盖伊·特立斯
      </span>
      <span class="publisher">
        上海人民出版社
      </span>
    </p>
  </div>
</div>
<div class="info">
  <div class="more-meta">
    <h4 class="title">
      深蓝的故事
    </h4>
    <p>
      <span class="author">
        深蓝
      </span>
      <span class="publisher">
        新星出版社
      </span>
    </p>
  </div>
</div>
'''

results = re.findall('"title">(.*?)</h4>.*?"author">(.*?)</span>.*?"publisher">(.*?)</span>', content, re.S)
for result in results:
    title, author, publisher = result
    print('title:', title.strip())
    print('author:', author.strip())
    print('publisher:', publisher.strip())

title: 邻人之妻
author: [美] 盖伊·特立斯
publisher: 上海人民出版社
title: 深蓝的故事
author: 深蓝
publisher: 新星出版社

---

re.sub()

re.sub 替换字符串中每一个匹配的子串后返回替换后的整个字符串

import re

content = 'hei, stt Hello 12345 World_This is Regex Demo'
content = re.sub('\d+', 'str', content)
print(content)

hei, stt Hello str World_This is Regex Demo

如果我们要替换的字符串包含它本身，我们可以给它用小括号分组，然后用反斜杠数字来引用

import re

content = 'hei, stt Hello 12345 World_This is Regex Demo'
content = re.sub('(\d+)', r'\1 678910', content)
print(content)

hei, stt Hello 12345 678910 World_This is Regex Demo

---

re.compile()

re.compile 将正则表达式编译成正则对象
只需要一次编译，就可以达到反复使用

import re

content = '''hei, stt Hello 12345 World_This 
is Regex Demo'''
pattern = re.compile('h.*?Demo', re.S)
result = pattern.match(content)
print(result)

<_sre.SRE_Match object; span=(0, 46), match='hei, stt Hello 12345 World_This \nis Regex Demo'>