正则表达式查找以特定字母开头或结尾的单词

Question

编写一个函数getWords(sentence, letter)，该函数接受一个句子和一个字母，并返回以该字母开头或结尾的单词列表，但不能同时返回，无论字母大小写。

例如：

>>> s = "The TART program runs on Tuesdays and Thursdays, but it does not start until next week."
>>> getWords(s, "t")
['The', 'Tuesdays', 'Thursdays', 'but', 'it', 'not', 'start', 'next']

我的尝试：

regex = (r'[\w]*'+letter+r'[\w]*')
return (re.findall(regex,sentence,re.I))

我的输出：

['The', 'TART', 'Tuesdays', 'Thursdays', 'but', 'it', 'not', 'start', 'until', 'next']

Answer 1

\b检测断字。详细模式允许多行正则表达式和注释。请注意，[^\W]与 相同\w，但要匹配\w某个字母，您需要[^\W{letter}].

import re

def getWords(s,t):
    pattern = r'''(?ix)           # ignore case, verbose mode
                  \b{letter}      # start with letter
                  \w*             # zero or more additional word characters
                  [^{letter}\W]\b # ends with a word character that isn't letter
                  |               #    OR
                  \b[^{letter}\W] # does not start with a non-word character or letter
                  \w*             # zero or more additional word characters
                  {letter}\b      # ends with letter
                  '''.format(letter=t)
    return re.findall(pattern,s)

s = "The TART program runs on Tuesdays and Thursdays, but it does not start until next week."
print(getWords(s,'t'))

输出：

['The', 'Tuesdays', 'Thursdays', 'but', 'it', 'not', 'start', 'next']