code: def get_parent_and_child(self, table_name):
          
          if table_name not in self.ancestry:
              return None, None
          parent_ind = self.ancestry.index(table_name) + 1
          if parent_ind + 1 > len(self.ancestry):
              parent_name = None
          else:
              parent_name = self.ancestry[parent_ind]
          child_ind = self.ancestry.index(table_name) - 1
          if child_ind < 0:
              child_name = None
          else:
              child_name = self.ancestry[child_ind]
          return parent_name, child_name
docs: Get the name of the parent table and the child table
          for a given MagIC table name.
  
          Parameters
          ----------
          table_name : string of MagIC table name ['specimens', 'samples', 'sites', 'locations']
  
          Returns
          -------
          parent_name : string of parent table name
          child_name : string of child table name