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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 attach(self, num_name, write=0):
 """Locate an existing vdata or create a new vdata in the HDF file, returning a VD instance. Args:: num_name Name or reference number of the vdata. An existing vdata can be specified either through its reference number or its name. Use -1 to create a new vdata. Note that uniqueness is not imposed on vdatas names, whereas refnums are guaranteed to be unique. Thus knowledge of its reference number may be the only way to get at a wanted vdata. write Set to 0 to open the vdata in read-only mode, set to 1 to open it in write mode Returns:: VD instance representing the vdata C library equivalent : VSattach After creating a new vdata (num_name == -1), fields must be defined using method fdefine() of the VD instance, and those fields must be allocated to the vdata with method setfields(). Same results can be achieved, but more simply, by calling the create() method of the VS instance. """


        mode = write and 'w' or 'r'
        if isinstance(num_name, str):
            num = self.find(num_name)
        else:
            num = num_name
        vd = _C.VSattach(self._hdf_inst._id, num, mode)
        if vd < 0:
            _checkErr('attach', vd, 'cannot attach vdata')
        return VD(self, vd)