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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 _load_metadata(self):
 """load metadata only if needed"""

        if self._schema is None:
            self._schema = self._get_schema()
            self.datashape = self._schema.datashape
            self.dtype = self._schema.dtype
            self.shape = self._schema.shape
            self.npartitions = self._schema.npartitions
            self.metadata.update(self._schema.extra_metadata)