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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def prepend_zeros_to_lists(ls):
 """ Takes a list of lists and appends 0s to the beggining of each sub_list until they are all the same length. Used for sign-extending binary numbers. """

    longest = max([len(l) for l in ls])

    for i in range(len(ls)):
        while len(ls[i]) < longest:
            ls[i].insert(0, "0")