r regex keep a character while substitue what comes first code example

Example 1: how to get just the filename in python

import os
>>> base=os.path.basename('/root/dir/sub/file.ext')
>>> base
'file.ext'
>>> os.path.splitext(base)
('file', '.ext')
>>> os.path.splitext(base)[0]
'file'

Example 2: how to compare a string with its ending in javascript

function solution(str, ending){
  return str.indexOf(ending, str.length - ending.length) !== -1;
}