Assuming Benoît Latinier’s interpretation of your question is right (which, it looks like it is), then there will be some cases where a unique letter can’t be found, and in these cases you might throw an exception:
def unique_chars(words):
taken = set()
uniques = []
for word in words:
for char in word:
if char not in taken:
taken.add(char)
uniques.append(char)
break
else:
raise ValueError("There are no unique letters left!")
return uniques
solved Is there a way in python to compare strings for unique character [closed]