• Solved the the task, but there is a problem

Question related to mission Non-unique Elements

def checkio(*data):
total = []
result = []
for i in data:
for y in total:
    ctr = total.count(y)
    if ctr > 1:
return result

the compilator on the site puts square brackets between values of my function, that's why my code doesn't work properly. It works fine without them. How to fix it? Thank you in advance.