How to find a phrase that is NOT at a word boundary from a string in Regex?

Question

Okay so this may be just googling wrong or not reading documentation correctly, but I couldn't find anything on this.

Say I have:

sample_str = "rose aaron robert moro"
pat = 'ro'

I want to find all instances of words (preferably using re.search()) which DON'T end OR begin in 'ro'. That is, I want one or more character to be before and after 'ro'. So I would want 'aaron' to match, but not at any of the other words in sample_str.

How would I do this? I tried a bunch of things, including '+ro+', but it gave me an error. I am not new to Python but have some trouble with the Regex, so if anyone can please explain that would be great.

Thanks

Answer 1

I believe you can use a negative look-ahead/look-behind for this.

\b(?!ro)\w+(?<!ro)\b

When applied to rose aaron robert moro will match only aaron.

Explanation

\b = a word boundary
(?!ro) = not followed by ro
\w+ = one or more word characters
(?<!ro)\b = another word boundary, not preceded by ro

Working Example

https://regex101.com/r/WcSlsx/2/