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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 diff(a, b):
 """ Performs a longest common substring diff. :Parameters: a : sequence of `comparable` Initial sequence b : sequence of `comparable` Changed sequence :Returns: An `iterable` of operations. """

    a, b = list(a), list(b)
    opcodes = SM(None, a, b).get_opcodes()
    return parse_opcodes(opcodes)