簡(jiǎn)單記錄下python下正則表達(dá)式的用法龄恋，加深對(duì)正則表達(dá)式用法的記憶，方便以后爬蟲
本文選取了莫煩python中我覺得常用的正則表達(dá)式的用例凶伙，如有希望更加全面了解python正則表達(dá)式的用法郭毕，可以點(diǎn)擊鏈接
python下簡(jiǎn)單的匹配
var1 = "i"
var2 = "she"
str = "i miss you"
print(var1 in str)
print(var2 in str)
運(yùn)行結(jié)果
True
False
Regex下簡(jiǎn)單匹配
import re
var1 = "i"
var2 = "she"
str = "i miss you"
print(re.search(var1, str))
print(re.search(var2, str))
運(yùn)行結(jié)果
<re.Match object; span=(0, 1), match='i'>
None
靈活匹配
需要找到潛在的可能性文件，可以通過[]將可能的字符囊括進(jìn)來函荣，通過r"expression"來表明這是一個(gè)正則表達(dá)式
"""例1"""
"""[au]表示a和u中可選取一個(gè)來進(jìn)行匹配"""
import re
print(re.search(r"r[au]n", "dog runs to cat"))
運(yùn)行結(jié)果
<re.Match object; span=(4, 7), match='run'>
"""例2"""
"""[a-z]表示所有小寫字母"""
"""[a-z0-9]表示所有數(shù)字和小寫字母"""
import re
print(re.search(r"r[a-z]n", "dog runs to cat"))
print(re.search(r"r[a-z0-9]n", "dog runs to cat")
運(yùn)行結(jié)果
<re.Match object; span=(4, 7), match='run'>
<re.Match object; span=(4, 7), match='run'>
轉(zhuǎn)義字符
- \d : 任何數(shù)字
- \D : 非數(shù)字
- \s : 任何 white space, 如 [\t\n\r\f\v]
- \S : 不是 white space
- \w : 任何大小寫字母, 數(shù)字和 “” [a-zA-Z0-9]
- \W : 不是 \w
- \b : 空白字符 (只在某個(gè)字的開頭或結(jié)尾)
- \B : 空白字符 (不在某個(gè)字的開頭或結(jié)尾)
- \ : 匹配 \
- . : 匹配任何字符 (除了 \n)
- ^ : 匹配開頭
- $ : 匹配結(jié)尾
- ? : 前面的字符可有可無
# \d : decimal digit
print(re.search(r"r\dn", "run r4n")) # <_sre.SRE_Match object; span=(4, 7), match='r4n'>
# \D : any non-decimal digit
print(re.search(r"r\Dn", "run r4n")) # <_sre.SRE_Match object; span=(0, 3), match='run'>
# \s : any white space [\t\n\r\f\v]
print(re.search(r"r\sn", "r\nn r4n")) # <_sre.SRE_Match object; span=(0, 3), match='r\nn'>
# \S : opposite to \s, any non-white space
print(re.search(r"r\Sn", "r\nn r4n")) # <_sre.SRE_Match object; span=(4, 7), match='r4n'>
# \w : [a-zA-Z0-9_]
print(re.search(r"r\wn", "r\nn r4n")) # <_sre.SRE_Match object; span=(4, 7), match='r4n'>
# \W : opposite to \w
print(re.search(r"r\Wn", "r\nn r4n")) # <_sre.SRE_Match object; span=(0, 3), match='r\nn'>
# \b : empty string (only at the start or end of the word)
print(re.search(r"\bruns\b", "dog runs to cat")) # <_sre.SRE_Match object; span=(4, 8), match='runs'>
# \B : empty string (but not at the start or end of a word)
print(re.search(r"\B runs \B", "dog runs to cat")) # <_sre.SRE_Match object; span=(8, 14), match=' runs '>
# \\ : match \
print(re.search(r"runs\\", "runs\ to me")) # <_sre.SRE_Match object; span=(0, 5), match='runs\\'>
# . : match anything (except \n)
print(re.search(r"r.n", "r[ns to me")) # <_sre.SRE_Match object; span=(0, 3), match='r[n'>
# ^ : match line beginning
print(re.search(r"^dog", "dog runs to cat")) # <_sre.SRE_Match object; span=(0, 3), match='dog'>
# $ : match line ending
print(re.search(r"cat$", "dog runs to cat")) # <_sre.SRE_Match object; span=(12, 15), match='cat'>
# ? : may or may not occur
print(re.search(r"Mon(day)?", "Monday")) # <_sre.SRE_Match object; span=(0, 6), match='Monday'>
print(re.search(r"Mon(day)?", "Mon")) # <_sre.SRE_Match object; span=(0, 3), match='Mon'>
重復(fù)匹配
- *：重復(fù)零次或多次
- +：重復(fù)一次或多次
- {n,m}：重復(fù)n次至m次
- {n}：重復(fù)n次
# * : occur 0 or more times
print(re.search(r"ab*", "a")) # <_sre.SRE_Match object; span=(0, 1), match='a'>
print(re.search(r"ab*", "abbbbb")) # <_sre.SRE_Match object; span=(0, 6), match='abbbbb'>
# + : occur 1 or more times
print(re.search(r"ab+", "a")) # None
print(re.search(r"ab+", "abbbbb")) # <_sre.SRE_Match object; span=(0, 6), match='abbbbb'>
# {n, m} : occur n to m times
print(re.search(r"ab{2,10}", "a")) # None
print(re.search(r"ab{2,10}", "abbbbb")) # <_sre.SRE_Match object; span=(0, 6), match='abbbbb'>
后面的內(nèi)容其實(shí)是對(duì)前面內(nèi)容的組合復(fù)用
分組
match = re.search(r"(\d+), Date: (.+)", "ID: 021523, Date: Feb/12/2017")
print(match.group()) # 021523, Date: Feb/12/2017
print(match.group(1)) # 021523
print(match.group(2)) # Date: Feb/12/2017
組會(huì)多的時(shí)候显押，有可能難以找到自己想要的組，這時(shí)候可以利用類似字典的原理傻挂，用名字構(gòu)建索引
match = re.search(r"(?P<id>\d+), Date: (?P<date>.+)", "ID: 021523, Date: Feb/12/2017")
print(match.group('id')) # 021523
print(match.group('date')) # Date: Feb/12/2017
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