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Python学习day19-常用模块之re模块
正则表达式
正则表达式我们应该或多或少都听过，因为这并不是python所独有的东西，而是一个比较广泛的概念。简单来说正则表达式就是从字符串里寻找特定的字符串，通过各种通配符和表达式。在Python中，正则表达式通过内嵌集成成为一个re模块，就是用来实现正则表达式的各种功能。
正则表达式的大致匹配过程是：依次拿出表达式中的字符来和文本中的字符进行比较，如果每一个字符都能匹配，则匹配成功，一旦有匹配不成功的字符则匹配失败。且一旦匹配成功就会跳过这个字符，并不会重复取值。
re的基本语法(匹配规则)：
re的语法很多，我们这里只介绍比较常用的一部分语法的用法：
xxxxxxxxxx
import re
s = '王大炮打炮被大炮打死了王大炮打炮被大炮打死了'
# 正常情况下，如果我们想要取出'大炮'这个字符只能用一下这种方法
print(s[1:3], s[6:8])
# 可见这非常的复杂，而且非常low
# 所以调用re模块来做的话，就像以下这样
res = re.findall('大炮',s)
print(res)# 这样我们就可以直接找到字符串里的所有‘大炮’的字符
# 另外还有一些别的用法
# ^:判定开头，注意要放在字符串前面，不会往后寻找，只会判定开头
print(re.findall('^王大炮', s))
# 即返回结果'王大炮'，因为字符串开头就是王大炮
# $:结尾，要注意放在字符串后面，和^相反
print(re.findall('死了$', s))
#返回结果是'死了'
# []:匹配中间的字符
s = 'abcdef'
print(re.findall('[ace]', s)) # 只要单个字符
# ['a', 'c', 'e']
# 返回的是分开的单个字符，且只要单个字符
# []+^:取反，^对[]内的元素，除了这些字符，输出其余的
print(re.findall('[^acef]', s))
# ['b','d']
# .：任意单个字符（除了换行符\n，如果需要取换行符，需要在字符串前面加r）
s = 'ababadaeaf'
print(re.findall('a.', s))
print(re.findall('a..', s))
# ['ab', 'ab', 'ad', 'ae', 'af']
# ['aba', 'ada']这个结果说明字符串里取过的字符不会重复取，只会取第一次
# *:可以替代字符0-无穷，都取出来，中间是空字符
s = 'abaacaaaaa'
print(re.findall('a*',s))
# ['a', '', 'aa', '', 'aaaaa', '']即但凡有a的地方都输出，没有的话就返回空数据
# +：前面的字符1-无穷，都取出来
print(re.findall('a+',s))
# ['a', 'aa', 'aaaaa']这种情况不存在空的情况，即最少为1个字符才会进行输出
# ?:前面的字符0-1个，即输出的都是单个字符，如果不是给定值，就返回空值
print(re.findall('a?',s))
# ['a', '', 'a', 'a', '', 'a', 'a', 'a', 'a', 'a', '']
# {m}：前面的字符m个，括号里的数字即为保留的位数，所以输出是5个a，如果字符串里没有五个a，就会输出空
print(re.findall('a{5}',s))
# ['aaaaa']
# {n,m}:前面的字符2-3个
print(re.findall('a{2,3}', s))# 会往最大的m取，最小n为才会输出
# ['aa', 'aaa', 'aa']#会取最大的m，也就是说如果字符串里有长度超过m的字符，只会返回长度为m的，也就是三位的，然后重新计数。
# \d:数字
s = 's1+s*2-s+3/'
print(re.findall('\d',s))# 只会输出字符串内的数字类型
# ['1','2','3']
# \D:非数字
print(re.findall('\D',s))# 不会输出数字类型，其余均取出
# ['s', '+', 's', '*', '-', 's', '+', '/']
# \w:数字/字符/下划线 都会取出来
print(re.findall('\w',s))
# ['s','1','s','2','s','3']
# \W:非数字/字符/下划线 取出来
print(re.findall('\W',s))
# ['+','*','-','+','/']
# \s:空格/t/n
s = 'avc sdf fe'
print(re.findall('\s',s))
# ['','']
# \S:非 空格/t/n
print(re.findall('\S',s))
# ['a','v',c','s','d','f','f','e']
# \:把后面的字符取消特殊意义
s = 'aba\d'
print(re.findall(r'\\d', s))
# ['\\d']
# .*:有什么都要,贪婪，结果最大化
s = 'abcabc'
print(re.findall('a.*c', s))
# ['abcabc']
# .*?:非贪婪，最小化，找到符合条件就停止,*********这个应该是以后用的最多的正则表达式
print(re.findall('a.*?c', s))
# ['abc','abc']
# ()：匹配到结果后只要括号内的，不要外面的，但匹配的时候条件是要全引号里的
s = 'abacad'
print(re.findall('a(.)', s))#点表示a后面的一个字符，加括号表示只显示这一个字符
# ['b','c','d']
# A|B：A和B都要
print(re.findall('a|b', s))# a和b都要，单字符值
# ['a','b','a','a']
# re模块的方法
# re.complie，根据包含的正则表达式的字符串创建模式对象。
s = 'abc123def\n456'
print(re.findall('\d+', s))
com = re.compile('f.')
print(re.findall(com, s))
# ['123','456']
# []
# re.S:匹配里面的所有字符，包括换行
print(re.findall('f.', s, re.S))
# ['f\n']
# re.match()：从开头搜索，搜索到了就是有，没搜索到就是None
s = 'abc'
res = re.match('\d+',s)
print(res)
res.group()
# re.search():搜索第一个搜索结果，找到即停止
re0s = re.search('\d+',s)
print(res)
print(res.group())
# re.split():以匹配规则来切割
s = 'abc534adf235sdf4'
print(re.split('\d+', s))
# re.sub（）：按照匹配规则来替换**************************重要
print(re.sub('\d+','***',s))
# re.subn():按照匹配规则替换，并计数
print(re.subn('\d+','***',s))
# 分组:一个括号叫一个分组,并给每个分组起名,key:value?,django里URL分组
s = 'abc123edf456'
res = re.search('abc(?P<abc>\d+)edf(?P<edf>\d+)', s)
print(res.groupdict())