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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 concat_list(listA, listB, delim=' '):
 """ Concatenate list elements pair-wise with the delim character Returns the concatenated list Raises index error if lists are not parallel """


    # Lists must be of equal length.
    if len(listA) != len(listB):
        raise IndexError('Input lists are not parallel.')

    # Concatenate lists.
    listC = []
    for i in xrange(len(listA)):
        app = listA[i] + delim + listB[i]
        listC.append(app)

    return listC