原文链接：http://www.one2know.cn/nlp4/

• * + ?

  * ：0个或多个

  + ：1个或多个

  ? ：0个或1个

  re.search()函数，将str和re匹配，匹配正确返回True

  import re

  匹配函数，输入：文本，匹配模式（即re）

  def text_match(text,patterns):
  if re.search(patterns,text):
  return 'Found a match!'
  else:
  return 'Not matched!'

  测试

  print(text_match('ac','ab?'))
  print(text_match('abc','ab?'))
  print(text_match('abbc','ab?'))

  print(text_match('ac','ab')) print(text_match('abc','ab'))
  print(text_match('abbc','ab*'))

  print(text_match('ac','ab+'))
  print(text_match('abc','ab+'))
  print(text_match('abbc','ab+'))

  print(text_match('abbc','ab{2}'))

  print(text_match('aabbbbc','ab{3,5}?'))

输出：

Found a match!
Found a match!
Found a match!
Found a match!
Found a match!
Found a match!
Not matched!
Found a match!
Found a match!
Found a match!
Found a match!

• $ ^ .

  $ ：结尾

  ^ ：开头

  . ：除换行符以外的任何字符

  \w ：字母，数字，下划线

  \s ：空格符

  \S ：非空格符

  \b ：空格

  \B ：非空格

  import re
  def text_match(text,patterns):
  if re.search(patterns,text):
  return 'Found a match!'
  else:
  return 'Not matched!'

  任意以a开头，以c结尾

  print(text_match('abbc','^a.*c$'))

  以文本开始，后面有出现一次或多次的文本

  print(text_match('Tuffy eats pie, Loki eats peas!','^\w+'))

  文末一个或多个\w加上0个或多个非空字符，\S在\w后面表示标点符号

  print(text_match('Tuffy eats pie, Loki eats peas!','\w+\S*$'))

  含u在中间的单词

  print(text_match('Tuffy eats pie, Loki eats peas!','\Bu\B'))

输出：

Found a match!
Found a match!
Found a match!
Found a match!

• 字符串匹配

  re.search(pattern,text) ：判断text里是否有pattern

  re.finditer(pattern,text) ：在text里找到pattern

  import re

  patterns = ['Tuffy','Pie','Loki']
  text = 'Tuffy eats pie, Loki eats peas!'

  匹配字符串

  for pattern in patterns:
  print('Searching for "%s" in "%s" ->' % (pattern,text))
  if re.search(pattern,text):
  # 如果不想区分大小写，加参数 flags=re.IGHORECASE
  print('Found!')
  else:
  print('Not Found!')

  匹配字符串，并找到他的位置

  pattern = 'eats'
  for match in re.finditer(pattern,text):
  s = match.start()
  e = match.end()
  print('Found "%s" at %d:%d'%(text[s:e],s,e))

输出：

Searching for "Tuffy" in "Tuffy eats pie, Loki eats peas!" ->
Found!
Searching for "Pie" in "Tuffy eats pie, Loki eats peas!" ->
Not Found!
Searching for "Loki" in "Tuffy eats pie, Loki eats peas!" ->
Found!
Found "eats" at 6:10
Found "eats" at 21:25

• 日期，一组字符集合(或字符范围)

  \d ：数字

  re.compile() ：string => RegexObject的对象

  方括号[]内的所有内容都是OR关系

  import re
  url = 'http://www.awdawd.com/da/wda/2019/7/2/wda.html'

  YYYY/MM/DD

  date_regex = '/(\d{4})/(\d{1,2})/(\d{1,2})'
  print('Data found in the URL :',re.findall(date_regex,url))

  有特殊字符返回Flase

  def is_allowed_specific_char(string):
  charRe = re.compile(r'[^a-zA-Z0-9.]')
  string = charRe.search(string)
  return not bool(string)

  print(is_allowed_specific_char('adIDHihdHDIh.'))
  print(is_allowed_specific_char('*#$%^&!{}'))

输出：

Data found in the URL : [('2019', '7', '2')]
True
False

• 找到所有长度为5的单词，缩写替换单词

  import re

  用缩写替换

  street = '21 Ramkrishna Road'
  print(re.sub('Road','Rd',street))

  找到长度为5的单词

  text = 'Tuffy eats pie, Loki eats bread!'
  print(re.findall(r'\b\w{5}\b',text))

输出：

21 Ramkrishna Rd
['Tuffy', 'bread']

• 基于RE的分词器

  import re

  raw = 'I am big! It\'s the pictures that got small.'

  用一个或多个空格分词

  print(re.split(r' +',raw))

  非 字母数字下划线 分词

  print(re.split(r'\W+',raw))

  匹配分词 ！

  print(re.findall(r'\w+|\S\w*',raw))

输出：

['I', 'am', 'big!', "It's", 'the', 'pictures', 'that', 'got', 'small.']
['I', 'am', 'big', 'It', 's', 'the', 'pictures', 'that', 'got', 'small', '']
['I', 'am', 'big', '!', 'It', "'s", 'the', 'pictures', 'that', 'got', 'small', '.']

• 基于RE的词干提取器

  import re

  自己的词干提取器

  def stem(word):
  split = re.findall(r'^(.*?)(ing|ly|ed|ies|ive|es|s|ment)?$',word)
  stem = split[0][0]
  return stem

  上节中re分词

  raw = 'Keep your friends close, but your enemies closer.'
  tokens = re.findall(r'\w+|\S\w*',raw)
  print(tokens)

  测试

  for t in tokens:
  print("'",stem(t),"'")

输出：

['Keep', 'your', 'friends', 'close', ',', 'but', 'your', 'enemies', 'closer', '.']
' Keep ' ' your ' ' friend ' ' close ' ' , ' ' but ' ' your ' ' enem ' ' closer ' ' . '