问题
Im trying to do something fairly simple with regular expression in python... thats what i thought at least.
What i want to do is matching words from a string if its preceded and followed by a whitespace. If its at the beginning of the string there is no whitespace required before - if its at the end, dont't search for whitespace either.
Example:
"WordA WordB WordC-WordD WordE"
I want to match WordA WordB WordE.
I only came up with overcomplicated way of doing this...
(?<=(?<=^)|(?<=\s))\w+(?=(?=\s)|(?=$))
It seems to me there has to be a simple way for such a simple problem....
I figured i can just start with (?<=\s|^) but that doesnt seem possible because "look-behind requires fixed-width pattern".
回答1:
You seem to work in Python as (?<=^|\s) is perfectly valid in PCRE, Java and Ruby (and .NET regex supports infinite width lookbehind patterns).
Use
(?<!\S)\w+(?!\S)
It will match 1 or more word chars that are enclosed with whitespace or start/end of string.
See the regex demo.
Pattern details:
(?<!\S)- a negative lookbehind that fails the match once the engine finds a non-whitespace char immediately to the left of the current location\w+- 1 or more word chars(?!\S)- a negative lookahead that fails the match once the engine finds a non-whitespace char immediately to the right of the current location.
来源：https://stackoverflow.com/questions/45189706/regular-expression-matching-words-between-white-space