code: def active_qubits(linear, quadratic):
      
  
      active = {idx for idx,bias in uniform_iterator(linear)}
      for edge, _ in six.iteritems(quadratic):
          active.update(edge)
      return active
docs: Calculate a set of all active qubits. Qubit is "active" if it has
      bias or coupling attached.
  
      Args:
          linear (dict[variable, bias]/list[variable, bias]):
              Linear terms of the model.
  
          quadratic (dict[(variable, variable), bias]):
              Quadratic terms of the model.
  
      Returns:
          set:
              Active qubits' indices.