def diff(li1, li2): 
    """
    used to return difference between two lists
    commonly used for when HFSS doesn't return the name of objects, for example
    when an stl file is imported, this function can be used to compare list
    of objects before and after import to return the list of imported objects

    returns: difference between lists
    """
    li_dif = [i for i in li1 + li2 if i not in li1 or i not in li2] 
    return li_dif