python之正則表達式

看了b站莫(da)煩(lao)的視頻，感受很詳細，本身手敲了一遍，方便你們查看，回頭忘了就過來看看。

點擊https://www.bilibili.com/video/av16926522/?p=36能夠去b站看dalao視頻python

# 1 匹配字符串中的目標字符串
pattern1 = "cat"
pattern2 = "bird"
string = "dog runs to cat"
print(re.search(pattern1, string))
print(re.search(pattern2, string))

#result
<re.Match object; span=(12, 15), match='cat'>
None

#2 匹配多種可能
ptn = r"r[au]n"
string = "dog runs(ran) to cat"
print(re.search(ptn, string))

#result
<re.Match object; span=(4, 7), match='run'>
#發現結果只返回匹配第一個檢索到的字符串

#3 匹配更多可能
print(re.search(r"r[A-Z]n", "dog runs to cat"))
print(re.search(r"r[a-z]n", "dog runs to cat"))
print(re.search(r"r[0-9]n", "dog r2ns to cat"))
print(re.search(r"r[0-9a-z]n", "dog runs to cat"))

#result
None
<re.Match object; span=(4, 7), match='run'>
<re.Match object; span=(4, 7), match='r2n'>
<re.Match object; span=(4, 7), match='run'>

#4 \d:數字， \D:非數字
print(re.search(r"r\dn", "run r4n"))
print(re.search(r"r\Dn", "run r4n"))

#result
<re.Match object; span=(4, 7), match='r4n'>
<re.Match object; span=(0, 3), match='run'>

#5 空白：\s, 非空白：\S 
#[\t\n\r\f\v]
print(re.search(r"r\sn", "r\nn r4n"))
print(re.search(r"r\Sn", "r\nn r4n"))

#result
<re.Match object; span=(0, 3), match='r\nn'>
<re.Match object; span=(4, 7), match='r4n'>

#6 全部字母數字和"_"
#\w:[a-zA-Z0-9_], \W相反
print(re.search(r"r\wn", "r\nn r4n"))
print(re.search(r"r\Wn", "r\nn r4n"))

#result
<re.Match object; span=(4, 7), match='r4n'>
<re.Match object; span=(0, 3), match='r\nn'>

#7 空白字符
#\b:僅僅在開始或結只有一個空白字符,\B反之
print(re.search(r"\b runs \b", "dog runs to cat"))
print(re.search(r"\B runs \B", "dog runs to cat"))

#result
<re.Match object; span=(3, 9), match=' runs '>
<re.Match object; span=(4, 10), match=' runs '>

#8 匹配特殊字符
#\\:匹配\, .匹配除了\n
print(re.search(r"runs\\", "dog runs\ to cat"))
print(re.search(r"r.n", "r\"n to cat"))

#result
<re.Match object; span=(4, 9), match='runs\\'>
<re.Match object; span=(0, 3), match='r"n'>

#9 ^: 句首， $: 句尾
print(re.search(r"^dog", "dog runs\ to cat"))
print(re.search(r"cat$", "r\"n to cat"))

#result
<re.Match object; span=(0, 3), match='dog'>
<re.Match object; span=(7, 10), match='cat'>

#10 ？：是否
print(re.search(r"Mon(day)?", "Monday"))
print(re.search(r"Mon(day)?", "Mon"))

#result
<re.Match object; span=(0, 6), match='Monday'>
<re.Match object; span=(0, 3), match='Mon'>

#11 多行匹配 Multi-line
string = ''' Dog runs to the cat. I run to the dog. '''
print(re.search(r"^I", string))
print(re.search(r"^I", string, flags= re.M))

#result
None
<re.Match object; span=(22, 23), match='I'>

#12 *：0或屢次
print(re.search(r"ab*", "a"))
print(re.search(r"ab*", "abbbbbbb"))

#result
<re.Match object; span=(0, 1), match='a'>
<re.Match object; span=(0, 8), match='abbbbbbb'>

#13 +：1或屢次
print(re.search(r"ab+", "a"))
print(re.search(r"ab+", "ab"))

#result
None
<re.Match object; span=(0, 2), match='ab'>

#14 可選次數{n,m}
print(re.search(r"ab{2,10}", "a"))
print(re.search(r"ab{2,10}", "abbbb"))

#result
None
<re.Match object; span=(0, 5), match='abbbb'>

#15 group組
match = re.search(r"(\d+), Date: (.+)", "ID: 21321, Date: Aug/19/2019")
print(match.group())
print(match.group(1))
print(match.group(2))

#result
21321, Date: Aug/19/2019
21321
Aug/19/2019

#16 ？P<name>: 組命名
match = re.search(r"(?P<id>\d+), Date: (?P<date>.+)", "ID: 21321, Date: Aug/19/2019")
print(match.group())
print(match.group('id'))
print(match.group('date'))

#result
21321, Date: Aug/19/2019
21321
Aug/19/2019

#17 findall: 尋找全部匹配
print(re.findall(r"r[au]n", "run ran ren"))

#result
['run', 'ran']

#18 |: 或
print(re.findall(r"r(a|u)n", "run ran ren"))

#result
['u', 'a']

#19 sub: 替換
print(re.sub(r"r[au]n", "catches", "dog runs to cat"))

#result
dog catchess to cat

#20 分裂
print(re.split(r"[,;\.]", "a,b;d.c"))

#result
['a', 'b', 'd', 'c']

#21 compile : 編譯
compile_re = re.compile(r"r[au]n")
print(compile_re.search("dog ran to cat"))

#result
<re.Match object; span=(4, 7), match='ran'>

另外，Python默認的是貪婪匹配，返回匹配結果最長的字符串。好比：web

import re
match = re.search(r'py.*?n', 'pyanbncndn')
print(match.group(0))

#result
pyanbncndn

而要想使用最小匹配，則只需加一個？即：正則表達式

import re
match = re.search(r'py.*?n', 'pyanbncndn')
print(match.group(0))

#result
pyan

最小匹配操做符以下：
ide