code: def get_qubits(self, indices=True):
          
          qubits = set()
          for instr in self.instructions:
              if isinstance(instr, (Gate, Measurement)):
                  qubits |= instr.get_qubits(indices=indices)
          return qubits
docs: Returns all of the qubit indices used in this program, including gate applications and
          allocated qubits. e.g.
  
              >>> p = Program()
              >>> p.inst(("H", 1))
              >>> p.get_qubits()
              {1}
              >>> q = p.alloc()
              >>> p.inst(H(q))
              >>> len(p.get_qubits())
              2
  
          :param indices: Return qubit indices as integers intead of the
              wrapping :py:class:`Qubit` object
          :return: A set of all the qubit indices used in this program
          :rtype: set