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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 index(index, length):
 """Generates an index. :param index: The index, can be positive or negative. :param length: The length of the sequence to index. :raises: IndexError Negative indices are typically used to index a sequence in reverse order. But to use them, the indexed object must convert them to the correct, positive index. This function can be used to do this. """

    if index < 0:
        index += length
    if 0 <= index < length:
        return index
    raise IndexError()