1、什么是正则表达式?
正则表达式,又称规则表达式,是一门小型的语言,通常被用来检索、替换那些符合某个模式(规则)的文本。
2、匹配字符:
. 匹配除换行符以外的任意字符
w 匹配字母或数字或下划线或汉字
s 匹配任意的空白符
d 匹配数字
匹配单词的开始或结束
^ 匹配字符串的开始
$ 匹配字符串的结束
3、匹配次数:
* 重复零次或更多次
+ 重复一次或更多次
? 重复零次或一次
{n} 重复n次
{n,} 重复n次或更多次
{n,m} 重复n到m次
4、常用方法
4.1 match
从起始位置开始匹配,匹配成功返回一个对象,未匹配成功返回None
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match(pattern, string, flags=0) # pattern: 正则模型 # string : 要匹配的字符串 # falgs : 匹配模式 X VERBOSE Ignore whitespace and comments for nicer looking RE's. I IGNORECASE Perform case-insensitive matching. M MULTILINE "^" matches the beginning of lines (after a newline) as well as the string. "$" matches the end of lines (before a newline) as well as the end of the string. S DOTALL "." matches any character at all, including the newline. A ASCII For string patterns, make w, W, , B, d, D match the corresponding ASCII character categories (rather than the whole Unicode categories, which is the default). For bytes patterns, this flag is the only available behaviour and needn't be specified. L LOCALE Make w, W, , B, dependent on the current locale. U UNICODE For compatibility only. Ignored for string patterns (it is the default), and forbidden for bytes patterns.
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# 无分组 r = re.match("hw+", origin) print(r.group()) # 获取匹配到的所有结果 print(r.groups()) # 获取模型中匹配到的分组结果 print(r.groupdict()) # 获取模型中匹配到的分组结果 # 有分组 # 为何要有分组?提取匹配成功的指定内容(先匹配成功全部正则,再匹配成功的局部内容提取出来) r = re.match("h(w+).*(?P<name>d)$", origin) print(r.group()) # 获取匹配到的所有结果 print(r.groups()) # 获取模型中匹配到的分组结果 print(r.groupdict()) # 获取模型中匹配到的分组中所有执行了key的组 Demo
4.2 search
浏览整个字符串去匹配第一个,未匹配成功返回None
search(pattern, string, flags=0)
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r = re.search("aw+", origin) print(r.group()) # 获取匹配到的所有结果 print(r.groups()) # 获取模型中匹配到的分组结果 print(r.groupdict()) # 获取模型中匹配到的分组结果 # 有分组 r = re.search("a(w+).*(?P<name>d)$", origin) print(r.group()) # 获取匹配到的所有结果 print(r.groups()) # 获取模型中匹配到的分组结果 print(r.groupdict()) # 获取模型中匹配到的分组中所有执行了key的组
4.3 findall
findall,获取非重复的匹配列表;如果有一个组则以列表形式返回,且每一个匹配均是字符串;如果模型中有多个组,则以列表形式返回,且每一个匹配均是元祖;空的匹配也会包含在结果中
findall(pattern, string, flags=0)
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# 无分组 r = re.findall("aw+",origin) print(r) # 有分组 origin = "hello alex bcd abcd lge acd 19" r = re.findall("a((w*)c)(d)", origin) print(r)
4.4 sub
# sub,替换匹配成功的指定位置字符串
sub(pattern, repl, string, count=0, flags=0)
# pattern: 正则模型
# repl : 要替换的字符串或可执行对象
# string : 要匹配的字符串
# count : 指定匹配个数
# flags : 匹配模式
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# 与分组无关 origin = "hello alex bcd alex lge alex acd 19" r = re.sub("aw+", "999", origin, 2) print(r)
4.5 split
split,根据正则匹配分割字符串
split(pattern, string, maxsplit=0, flags=0)
pattern: 正则模型
string : 要匹配的字符串
maxsplit:指定分割个数
flags : 匹配模式
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origin = "hello alex bcd alex lge alex acd 19" r = re.split("alex", origin, 1) print(r) # 有分组 origin = "hello alex bcd alex lge alex acd 19" r1 = re.split("(alex)", origin, 1) print(r1) r2 = re.split("(al(ex))", origin, 1) print(r2)
4.6常用正则表达式
IP: ^(25[0-5]|2[0-4]d|[0-1]?d?d)(.(25[0-5]|2[0-4]d|[0-1]?d?d)){3}$ 手机号: ^1[3|4|5|8][0-9]d{8}$ 邮箱: [a-zA-Z0-9_-]+@[a-zA-Z0-9_-]+(.[a-zA-Z0-9_-]+)+
5、计算器实例代码:
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#!/usr/bin/env python # -*- coding:utf-8 -*- import re origin = "11+22-(33/3)+4+(12+(66/3))" # print(eval(origin)) #使用eval 方法 def f1(*args): ''' 计算()里面的内容 :param args: :return: ''' return 1 while True: result = re.split("(([^()]+))",origin,1) if len(result) == 3: before,content,after = result r = f1(content) new_str = before + str(r) + after origin = new_str print(origin) else: final = f1(origin) print(final) break