import re
sz = ["first_name last_name","last_name, first_name"]
for s in sz:
	m = re.search(r'(\w+),\s+(\w+)|(\w+)\s+(\w+)', s)
	if m:
		surname = "{}{}".format(m.group(1) or '', m.group(4) or '')
		name = "{}{}".format(m.group(2) or '', m.group(3) or '') 
		print("{} {}".format(name, surname))
	else:
		print("No match")