reversed_dict = {}
for value in list(mydict.values()):
    if value not in list(reversed_dict.keys()):
        reversed_dict[value] = []
for key in list(mydict.keys()):
    if mydict[key] == value:
        if key not in reversed_dict[value]:
            reversed_dict[value].append(key)
How to reverse a dictionary that it has repeated values (python)