网络爬虫-2:正则化
1.正则化
一.正则化
1.转义字符
| 转义字符 | 含义 |
|---|---|
\s | 空白字符（空格、制表符等） |
\d | 数字字符（0-9） |
\w | 字母、数字或下划线 |
. | 除换行符外的任意字符 |
\n | 换行符 |
\t | 制表符 |
import re
result = re.findall(r'\s', 'Hello World\nPython')
print(result) # 输出: [' ', '\n']
result = re.findall(r'\d', 'Python 3.10')
print(result) # 输出: ['3', '1', '0']
result = re.findall(r'\w', 'Python_3.10!')
print(result) # 输出: ['P', 'y', 't', 'h', 'o', 'n', '_', '3', '1', '0']
result = re.findall(r'P.th.n', 'Python Pathon Pithon')
print(result) # 输出: ['Python', 'Pathon', 'Pithon']
result = re.findall(r'\.', 'Python 3.10')
print(result) # 输出: ['.']2.转义字符
{} | 量词，指定匹配次数 |
* | 匹配前面的字符 0 次或多次 |
+ | 匹配前面的字符 1 次或多次 |
? | 匹配前面的字符 0 次或 1 次 |
$ | 匹配字符串结尾 |
|
| 匹配字符串开头 |
import re
result = re.findall(r'\d{3}', '123 4567 89')
print(result) # 输出: ['123', '456']
result = re.findall(r'ba*', 'ba baa baaa b')
print(result) # 输出: ['ba', 'baa', 'baaa', 'b']
result = re.findall(r'ba+', 'ba baa baaa b')
print(result) # 输出: ['ba', 'baa', 'baaa']
result = re.findall(r'ba?', 'ba baa baaa b')
print(result) # 输出: ['ba', 'ba', 'ba', 'b']
result = re.findall(r'world$', 'world1 hello world')
print(result) # 输出: ['world']
result = re.findall(r'^hello', 'hello world hello1')
print(result) # 输出: ['hello']1.re.match():仅从字符串开头
1.1常规匹配
re.match 是 Python 中 re 模块的一个函数，用于从字符串的起始位置匹配正则表达式。如果匹配成功，返回一个匹配对象；否则返回 None
import re
content="Hello 123 456789 World_This is a Regex Demo"
res=re.match("^Hello\s\d\d\d\s\d{6}\s\w{10}.*Demo$",content)
print(res) #返回一个匹配的对象
print(res.group())#获取匹配的内容
print(res.span()) #获取匹配长度
print(len(content))<re.Match object; span=(0, 43), match='Hello 123 456789 World_This is a Regex Demo'>
Hello 123 456789 World_This is a Regex Demo
(0, 43)
431.2泛匹配
content="Hello 123 456789 World_This is a Regex Demo"
res=re.match("He.*?Demo",content)
print(res)
print(res.group())
print(res.span())
print(len(content))<re.Match object; span=(0, 43), match='Hello 123 456789 World_This is a Regex Demo'>
Hello 123 456789 World_This is a Regex Demo
(0, 43)
431.3分组匹配
import re
content="Hello 123 456789 World_This is a Regex Demo"
res=re.match("Hello\s(\d+)\s(\d{3})\d{3}\s(\w+)",content)
print(res)
print(res.group())
print(res.group(1))
print(res.group(2))
print(res.group(3))<re.Match object; span=(0, 27), match='Hello 123 456789 World_This'>
Hello 123 456789 World_This
123
456
World_This1.4贪婪匹配:尽可能多的去匹配
import re
content="Hello 123 w 456789 World_This is a Regex Demo"
res = re.match("^Hello.*(\d+)\s",content)#最后的\s会匹配到一个空格
res2=re.match("^Hello.*(\d*)",content)
print(res)
print(res.group())
print(res.group(1))
a=res2.group(1)
if not a:
print("匹配到0个") <re.Match object; span=(0, 19), match='Hello 123 w 456789 '>
Hello 123 w 456789
9
匹配到0个
1.6非贪婪匹配:尽可能少的去匹配
.*?：非贪婪匹配任意字符（尽可能短）。.+?：非贪婪匹配至少一个任意字符。
import re
content="Hello 123 w 456789 World_This is a Regex Demo"
res = re.match("^Hello.*?(\d+)\s",content)
print(res)
print(res.group(1))<re.Match object; span=(0, 10), match='Hello 123 '>
123
1.6匹配模式
换行使用re.s或\n
import re
content=("""Hello 123 w 456789
World_This is a Regex Demo""")
res = re.match("^Hello.*Demo$",content,re.S)
res2=re.match("^Hello.*\n.*Demo$",content)
print(res)
print(res2)<re.Match object; span=(0, 45), match='Hello 123 w 456789\nWorld_This is a Regex Demo'>
<re.Match object; span=(0, 45), match='Hello 123 w 456789\nWorld_This is a Regex Demo'>1.7转义
在特殊字符前加\
import re
content="price is $5"
res=re.match("^price\s(.*)$5",content)
res1=re.match("^price\s(.*)\$5",content)
print(res)
print(res1)None
<re.Match object; span=(0, 11), match='price is $5'>2.re.search():搜索整个字符串
import re
content="Hello 123 w 456789 World_This is a Regex Demo price is $5"
res=re.search("price\s(.*)\$5$",content)
print(res)
print(res.group())
print(res.group(1))<re.Match object; span=(46, 57), match='price is $5'>
price is $5
is 3.re.findall():因为re.match()和re.search(),都只能查找到符合的第一个字符使用findall查找所有的符合标准的字符
import re
content="""
<div class="songlist__artist">
<a class="playlist__author" title="虞书欣" href="/n/ryqq/singer/0031rIlo4Xka96">虞书欣</a><!-- -->
/<a class="playlist__author" title="丁禹兮" href="/n/ryqq/singer/004fOu5r1U3AJh">丁禹兮</a><!-- -->
/<a class="playlist__author" title="祝绪丹" href="/n/ryqq/singer/003IHuTa1HGoKK">祝绪丹</a><!-- -->
/<a class="playlist__author" title="杨仕泽" href="/n/ryqq/singer/0007YOgR1AUf1l">杨仕泽</a><!-- -->
/<a class="playlist__author" title="费启鸣" href="/n/ryqq/singer/000ic7PL1ViRKA">费启鸣</a><!-- -->
/<a class="playlist__author" title="李奕臻" href="/n/ryqq/singer/001w0v9Z0P1YuO">李奕臻</a><!-- -->
/<a class="playlist__author" title="卢禹豪" href="/n/ryqq/singer/000bfUG63tBcwb">卢禹豪</a>
</div>
<div class="songlist__time">03:49</div>
"""
res=re.findall('<a class="playlist__author"\stitle="(.*?)"\shref="(.*?)">(.*?)</a>',content,re.S)
print(res)
for i in res:
print(i)4.re.sub:替换原文中的字符为新的字符串
import re
content="timme time timese"
res=re.sub("m","7",content)
print(res) #ti77e ti7e ti7ese