import copy


def list_inter(ls1, ls2):
    """
    return common elements between ls1 and ls2 
    """
    ls1 = list(dict.fromkeys(copy.deepcopy(ls1)).keys())
    ls2 = list(dict.fromkeys(copy.deepcopy(ls2)).keys())
    res = [i for i in ls1 if i in ls2]
    return res