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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 nbytes_stored(self):
 """The total number of stored bytes of data for the array. This includes storage required for configuration metadata and user attributes."""

        m = getsize(self._store, self._path)
        if self._chunk_store is None:
            return m
        else:
            n = getsize(self._chunk_store, self._path)
            if m < 0 or n < 0:
                return -1
            else:
                return m + n