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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 next(self, vRef):
 """Get the reference number of the vdata following a given vdata. Args:: vRef Reference number of the vdata preceding the one we require. Set to -1 to get the first vdata in the HDF file. Knowing its reference number, the vdata can then be opened (attached) by passing this reference number to the attach() method. Returns:: Reference number of the vdata following the one given by argument vref An exception is raised if no vdata follows the one given by vRef. C library equivalent : VSgetid """


        num = _C.VSgetid(self._hdf_inst._id, vRef)
        _checkErr('next', num, 'cannot get next vdata')
        return num