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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 metadata(self):
 """Retrieves metadata about the object. Returns: An ObjectMetadata instance with information about this object. Raises: Exception if there was an error requesting the object's metadata. """

    if self._info is None:
      try:
        self._info = self._api.objects_get(self._bucket, self._key)
      except Exception as e:
        raise e
    return ObjectMetadata(self._info) if self._info else None