How to reverse a dictionary with repeated values as a set

I’ve tried flip my dict. If some keys have the same value the flipped dict key should be a set()

d = {'a': 1, 'b': 2, 'c': 3, 'd': 3}

output should be:

{1: 'a', 2: 'b', 3: {'c', 'd'}}

I’ve tried that:

d = {'a': 1, 'b': 2, 'c': 3, 'd': 3}
rev_dict = {}
for k, v in d.items():
    rev_dict.setdefault(v, set()).add(k)
print(rev_dict)

But I got that:

{1: {'a'}, 2: {'b'}, 3: {'c', 'd'}}

>Solution :

just create a new dictionary

newdict = {}
for key, val in d.items():
   if val not in newdict:
        newdict[val] = key
   else:
        newdict[val] = set((*newdict[val], key))