Python 正则表达式

from nltk.book import *
import nltk
import re
wordlist = [w for w in nltk.corpus.words.words('en') if w.islower()]

 Introductory Examples for the NLTK Book 
Loading text1, …, text9 and sent1, …, sent9
Type the name of the text or sentence to view it.
Type: 'texts()' or 'sents()' to list the materials.
text1: Moby Dick by Herman Melville 1851
text2: Sense and Sensibility by Jane Austen 1811
text3: The Book of Genesis
text4: Inaugural Address Corpus
text5: Chat Corpus
text6: Monty Python and the Holy Grail
text7: Wall Street Journal
text8: Personals Corpus
text9: The Man Who Was Thursday by G . K . Chesterton 1908

1开始^与结束\$

^匹配一个正则表达式的开始，\$匹配一个正则表达式的结束:

比如r’ed$’代表以ed结束的正则表达

regexp = r'ed$'
[w for w in wordlist if re.search(regexp,w)][0:10]

[u'abaissed',
 u'abandoned',
 u'abased',
 u'abashed',
 u'abatised',
 u'abed',
 u'aborted',
 u'abridged',
 u'abscessed',
 u'absconded']

或者匹配以aa开头的字符：

regexp = r'^aa'
[w for w in wordlist if re.search(regexp,w)]

[u'aa', u'aal', u'aalii', u'aam', u'aardvark', u'aardwolf']

2任意单个字符”.”和可选”?”

“.”代表任何单个字符

“?”代表之前一个字符是可以选择的，比如r’E-?mail’可以匹配到Email和E-mail

regexp = r'^b.t$'
[w for w in wordlist if re.search(regexp,w)]

[u'bat', u'bet', u'bit', u'bot', u'but']

regexp = r'e-?mail'
sum(1 for w in nltk.book.text5 if re.search(regexp,w))

3

3范围与闭包

范围

r’^[abc]’匹配以abc开头的字符括号中的字母顺序没有关系

r’^[a-d]’匹配以a-d开头的字符

闭包

‘+’ 代表一个或多个实例

‘*’ 代表0个或几个实例

chatWords = sorted(set(w for w in nltk.corpus.nps_chat.words()))
regexp = r'^[ha]+$'
[w for w in chatWords if re.search(regexp,w)][0:10]

[u'a',
 u'aaaaaaaaaaaaaaaaa',
 u'aaahhhh',
 u'ah',
 u'ahah',
 u'ahahah',
 u'ahh',
 u'ahhahahaha',
 u'ahhh',
 u'ahhhh']

regexp1 = r'^m+i+n+e+$'
[w for w in chatWords if re.search(regexp1,w)]

[u'miiiiiiiiiiiiinnnnnnnnnnneeeeeeeeee',
 u'miiiiiinnnnnnnnnneeeeeeee',
 u'mine',
 u'mmmmmmmmiiiiiiiiinnnnnnnnneeeeeeee']

regexp2 = r'^mine$'
[w for w in chatWords if re.search(regexp2,w)]

[u'',
 u'e',
 u'i',
 u'in',
 u'm',
 u'me',
 u'meeeeeeeeeeeee',
 u'mi',
 u'miiiiiiiiiiiiinnnnnnnnnnneeeeeeeeee',
 u'miiiiiinnnnnnnnnneeeeeeee',
 u'min',
 u'mine',
 u'mm',
 u'mmm',
 u'mmmm',
 u'mmmmm',
 u'mmmmmm',
 u'mmmmmmmmiiiiiiiiinnnnnnnnneeeeeeee',
 u'mmmmmmmmmm',
 u'mmmmmmmmmmmmm',
 u'mmmmmmmmmmmmmm',
 u'n',
 u'ne']

‘[^..]’括号中的^匹配所有不在其中的字符

比如匹配所有非元音字母：

regexp2 = r'^[^aeiouAEIOU]+$'
[w for w in wordlist if re.search(regexp2,w)][0:10]

[u'b', u'by', u'byth', u'c', u'cly', u'cry', u'crypt', u'cwm', u'cyp', u'cyst']

4其他需要用到的表达

• ‘\’转义，比如’.’匹配’.’,’\$’匹配‘\$’


• ‘|’表示选择，比如’(ed|ing)\$’代表以ed或者ing结尾的字符


• ‘{m,n}’表示重复次数，m到n次，左右可舍弃

wsj = sorted(set(nltk.corpus.treebank.words()))
[w for w in wsj if re.search('^[0-9]+.[0-9]+$',w)][1:10]

[u'0.05', u'0.1', u'0.16', u'0.2', u'0.25', u'0.28', u'0.3', u'0.4', u'0.5']

[w for w in wsj if re.search('^[A-Z]+\$$',w)]

[u'US$']

[w for w in wsj if re.search('^[0-9]{4}',w)][0:10]

[u'1614',
 u'1637',
 u'1738.1',
 u'1787',
 u'1901',
 u'1903',
 u'1917',
 u'1920s',
 u'1925']

[w for w in wsj if re.search('^[0-9]+-[a-z]{3,5}',w)][0:10]

[u'10-day',
 u'10-lap',
 u'10-year',
 u'100-megabyte',
 u'100-share',
 u'11-month-old',
 u'12-member',
 u'12-point',
 u'12-year',
 u'14-hour']

[w for w in wsj if re.search('[a-z]{5,}-[a-z]{2,3}-[a-z]',w)][0:10]

[u'black-and-white',
 u'bread-and-butter',
 u'father-in-law',
 u'machine-gun-toting',
 u'savings-and-loan',
 u'search-and-seizure',
 u'truth-in-lending']

[w for w in wsj if re.search('(ed|ing)$',w)][0:10]

[u'62%-owned',
 u'Absorbed',
 u'According',
 u'Adopting',
 u'Advanced',
 u'Advancing',
 u'Alfred',
 u'Allied',
 u'Annualized',
 u'Anything']