import re
strs = ['/home/me/data/dataset/images/dark-side_23----83971436re.jpg',
            '/home/me/data/dataset/images/medium-side_23---83971436re.jpg',
            '/home/me/data/dataset/images/others_23---83971436re.jpg',
            '/home/me/data/dataset/images/light-side_23---83971436re.jpg']
rx = re.compile(r'(?:(?:dark|medium)-)?([^/]+)_\d+---[^/]*\.jpg$')
for s in strs:
	m = rx.search(s)
	if m:
		print(m.group(1))