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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 parse(cls, fptr, offset, length):
 """Parse component mapping box. Parameters fptr : file Open file object. offset : int Start position of box in bytes. length : int Length of the box in bytes. Returns ------- ComponentMappingBox Instance of the current component mapping box. """

        num_bytes = offset + length - fptr.tell()
        num_components = int(num_bytes / 4)

        read_buffer = fptr.read(num_bytes)
        data = struct.unpack('>' + 'HBB' * num_components, read_buffer)

        component_index = data[0:num_bytes:3]
        mapping_type = data[1:num_bytes:3]
        palette_index = data[2:num_bytes:3]

        return cls(component_index, mapping_type, palette_index,
                   length=length, offset=offset)