正则表达式匹配前面的单词

Question

i'm attempting to extract the word 'Here' as 'Here' contains a capital letter at beginning of word and occurs before word 'now'.

Here is my attempt based on regex from :

regex match preceding word but not word itself

import re
sentence = "this is now test Here now tester"
print(re.compile('\w+(?= +now\b)').match(sentence))

None is printed in above example.

Have I implemented regex correctly ?

Answer 1

The following works for the given example:

Regex:

re.search(r'\b[A-Z][a-z]+(?= now)', sentence).group()

Output:

'Here'

Explanation:

\\b imposes word boundary

[AZ] requires that word begins with capital letter

[az]+ followed by 1 or more lowercase letters (modify as necessary)

(?= now) positive look-ahead assertion to match now with leading whitespace