Sort last

[pyzyx3qwerty]

I have been taking a class, so this must count as homework. So thing is given a list of non-empty tuples, return a list sorted in increasing order by the last element in each tuple. e.g. [(1, 7), (1, 3), (3, 4, 5), (2, 2)] yields [(2, 2), (1, 3), (3, 4, 5), (1, 7)] Hint: use a custom key= function to extract the last element form each tuple.
Here's my go :

def sort_last(tuples):
     for t in tuples :
          last_element = t[-1]
     return sorted(tuples, key = last)

Unfortunately, this is all i have been able to do. I don't know how can I sort the list on the basis of its last element in ascending order. Any help would be appreciated