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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 ref(self):
 """ A write-back version of Trace Returns ------- ref : RefTrace `ref` is returned in a context manager, and must be in a ``with`` statement Notes ----- .. versionadded:: 1.6 Examples -------- """


        x = RefTrace(self.filehandle,
                     self.dtype,
                     len(self),
                     self.shape,
                     self.readonly,
                    )
        yield x
        x.flush()