Regex for selecting words ending in 'ing' unless

Question

I want to select words ending in with a regular expression, but I want exclude words that end in thing. For example:

everything
running 
catching 
nothing

Of these words, running and catching should be selected, everything and nothing should be excluded.

I've tried the following:

.+ing$

But that selects everything. I'm thinking look aheads/look arounds could be the solution, but I haven't been able to get one that works.

Solutions that work in Python or R would be helpful.

Answer 1

In python you can use negative lookbehind assertion as this:

^.*(?<!th)ing$

RegEx Demo

(?<!th) is negative lookbehind expression that will fail the match if th comes before ing at the end of string.

Note that if you are matching words that are not on separate lines then instead of anchors use word boundaries as:

\w+(?<!th)ing\b