docs: def delete(self, symbol):
          """
          Delete all versions of the item from the current library which aren't
          currently part of some snapshot.
  
          Parameters
          ----------
          symbol : `str`
              symbol name to delete
          """
          logger.info("Deleting data item: %r from %r" % (symbol, self._arctic_lib.get_name()))
          # None is the magic sentinel value that indicates an item has been deleted.
          sentinel = self.write(symbol, None, prune_previous_version=False, metadata={'deleted': True})
          self._prune_previous_versions(symbol, 0)
  
          # If there aren't any other versions, then we don't need the sentinel empty value
          # so delete the sentinel version altogether
          snapped_version = self._versions.find_one({'symbol': symbol,
                                                     'metadata.deleted': {'$ne': True}})
          if not snapped_version:
              self._delete_version(symbol, sentinel.version)
          assert not self.has_symbol(symbol)