Вернуть массив, состоящий только из неуникальных элементов данного массива

#Your optional code here
#You can import some modules or create additional functions
 
 
def checkio(data):
    #Your code here
    #It's main function. Don't remove this function
    #It's used for auto-testing and must return a result for check.  
    data = [1, 2, 3, 1, 3]
    result = []
    for el in data:
        if data.count(el) > 1:
            result.append(el)
    return data
#Some hints
#You can use list.count(element) method for counting.
#Create new list with non-unique elements
#Loop over original list
 
 
if __name__ == "__main__":
    #These "asserts" using only for self-checking and not necessary for auto-testing
    assert isinstance(checkio([1]), list), "The result must be a list"
    assert checkio([1, 2, 3, 1, 3]) == [1, 3, 1, 3], "1st example"
    assert checkio([1, 2, 3, 4, 5]) == [], "2nd example"
    assert checkio([5, 5, 5, 5, 5]) == [5, 5, 5, 5, 5], "3rd example"
    assert checkio([10, 9, 10, 10, 9, 8]) == [10, 9, 10, 10, 9], "4th example"

def checkio(data):
    result = []
    for i in data:
        if data.count(i) > 1:
            result.append(i)
    return result
 
if __name__ == "__main__":
    assert isinstance(checkio([1]), list), "The result must be a list"
    assert checkio([1, 2, 3, 1, 3]) == [1, 3, 1, 3], "1st example"
    assert checkio([1, 2, 3, 4, 5]) == [], "2nd example"
    assert checkio([5, 5, 5, 5, 5]) == [5, 5, 5, 5, 5], "3rd example"
    assert checkio([10, 9, 10, 10, 9, 8]) == [10, 9, 10, 10, 9], "4th example"

def checkio(data):
    return [x for x in data if data.count(x) > 1]
 
if __name__ == "__main__":
    assert isinstance(checkio([1]), list), "The result must be a list"
    assert checkio([1, 2, 3, 1, 3]) == [1, 3, 1, 3], "1st example"
    assert checkio([1, 2, 3, 4, 5]) == [], "2nd example"
    assert checkio([5, 5, 5, 5, 5]) == [5, 5, 5, 5, 5], "3rd example"
    assert checkio([10, 9, 10, 10, 9, 8]) == [10, 9, 10, 10, 9], "4th example"