import string
def untokenize(tokens):
	return "".join([" "+i if not i.startswith("'") and i not in string.punctuation else i for i in tokens]).strip()

import string
def untokenize(tokens):
	#Joins all tokens in the list into a single string.
	#If a token doesn't start with an apostrophe and isn't a punctuation mark, add a space in front of it before joining.
	#Then strip the total string so that leading spaces and trailing spaces are removed.
	return "".join([" "+i if not i.startswith("'") and i not in string.punctuation else i for i in tokens]).strip()

Add comment clarifying how it operates.