python基础之re模块

时间:2021-01-23 22:34:59

就其本质而言,正则表达式(或 RE)是一种小型的、高度专业化的编程语言,(在Python中)它内嵌在Python中,并通过 re 模块实现。正则表达式模式被编译成一系列的字节码,然后由用 C 编写的匹配引擎执行。

正则就是给字符串操作得。
爬虫里会大量用到字符串。要处理一定是对字符串处理。

正则表达式是模糊匹配,这就是正则表达式得真正关键所在。

匹配是一个一个对应的关系,匹配上就放进自己的列表中。

 

字符匹配(普通字符,元字符):

1 普通字符:大多数字符和字母都会和自身匹配
              >>> re.findall('alvin','yuanaleSxalexwupeiqi')
                      ['alvin'] 

2 元字符:. ^ $ * + ? { } [ ] | ( ) \  #共11个元字符

python基础之re模块python基础之re模块
def findall(pattern, string, flags=0):
"""Return a list of all non-overlapping matches in the string.

If one or more capturing groups are present in the pattern, return
a list of groups; this will be a list of tuples if the pattern
has more than one group.

Empty matches are included in the result.
"""
return _compile(pattern, flags).findall(string)
findall剑谱

re.findall(pattern,string) #找到所有的匹配元素,返回列表

(1) . : 匹配除\n以外的任意符号

print(re.findall("a.+d","abcd"))

(2)^ :从字符串开始位置匹配

print(re.findall("^luchuan","luchuan123asd"))

(3)* + ? {} :重复

print(re.findall("[0-9]{4}","asd1231asd123"))
print(re.findall("[0-9]{1,}","asd1231asd123"))

贪婪匹配: #用得比较多

print(re.findall("\d+","af5324jh523hgj34gkhg53453"))

非贪婪匹配:

print(re.findall("\d+?","af5324jh523hgj34gkhg53453"))
print(re.findall("\d","af5324jh523hgj34gkhg53453"))

(4)字符集[]:起一个或者的意思

print(re.findall("a[bc]d","hasdabdjhacd"))

注意: *,+ .等元字符都是普通符号,- ^ \:

print(re.findall("[0-9]+","dash234sdfj223"))
print(re.findall("\d+","dash234sdfj223"))

print(re.findall("[a-z]+","dash234sdfj223"))

print(re.findall("[^2]","d2a2"))
print(re.findall("[^\d]","d2a2"))
print(re.findall("[^\d]+","d2a24sdf2ff23df21sfsf32d2d21d"))

(5)():分组

print(re.findall("(ad)+","addd"))
print(re.findall("(ad)+luchuan","adddluchuangfsdui"))
print(re.findall("(ad)+luchuan","adadluchuangfsdui")) #adadyuan都匹配到了,但是只把ad放进列表里了
print(re.findall("(?:ad)+luchuan","adadluchuangfsdui")) #取消组内优先级,将匹配所有匹配到得内容
print(re.findall("(\d)+luchuan","ad12343luchuangfs234dui"))
print(re.findall("(?:\d)+luchuan","ad12343luchuangfs234dui"))

命名分组:

ret=re.findall(r"\w+\.aticles\.\d{2}","lu.aticles.1234")
print(ret)
ret=re.findall(r"(\w+)\.aticles\.(\d{2})","lu.aticles.1234")
print(ret)
ret=re.search(r"(?P<author>\w+)\.aticles\.(?P<id>\d{2})","lu.aticles.1234") #命名分组,可以通过别名来取值
print(ret.group("id"))
print(ret.group("author"))

(6)| : 或

print(re.findall("www\.(oldboy|baidu)\.com","www.oldboy.com")) #不命名分组
print(re.findall("www\.(?:oldboy|baidu)\.com","www.oldboy.com"))

(7)\ : 转义

1 后面加一个元字符使其变成普通符号 \. \*
2 将一些普通符号变成特殊符号 比如 \d \w

print(re.findall("-?\d+\.?\d*\*\d+\.?\d*","-2*6+7*45+1.4*3-8/4"))
print(re.findall("\w","$da@s4 234"))
print(re.findall("a\sb","a badf"))
print(re.findall(r"\bI","hello I am LIA")) #ASCII码中有\b字符,所以需要原生字符
print(re.findall("\\bI","hello I am LIA"))
print(re.findall(r"\bI","hello$I am LIA"))
print(re.findall("c\\\\l","abc\l")) #python解释器默认会把\\解释成\,re模块又会把\\解释成\,所以需要四个
print(re.findall(r"c\\l","abc\l")) #告诉python解释器按照正则去匹配。
print(re.findall("\d+\.?\d*\*\d+\.?\d*","3.5*22+3*2+4.5*33-8+2"))

re的方法:

s=re.finditer("\d+","ad324das32")
print(s)

print(next(s).group()) #next后只是个对象,还需要进行操作
print(next(s).group())

search:只匹配第一个结果

ret=re.search("\d","jksf34asd3") #使用search做计算器
print(ret)
print(ret.group()) #通过group()取值,None得话是匹配未成功

match:只在字符串开始的位置匹配

ret=re.match("\d+","432jksf34asd3")
print(ret)
print(ret.group())

split:拆分

s2=re.split("\d+","fh233jfd324sfsa213190sdf",2)
print(s2)

ret3=re.split("l","hello luchuan")
print(ret3)

re.sub:替换

ret4=re.sub("\d+","A","hello 234jkhh23")
ret4=re.sub("\d+","A","hello 234jkhh23",1)
print(ret4)

re.subn:

ret4=re.subn("\d+","A","hello 234jkhh23")
print(ret4)

compile :编译方法,一次得话,没什么意义,匹配多个字符串就有意义了

c=re.compile("\d+")
ret5=c.findall("hello32world53")
print(ret5)

 

链接:http://www.cnblogs.com/yuanchenqi/articles/5732581.html