code: def pauli_string(self, qubits=None):
          
          if qubits is None:
              warnings.warn("Please provide a list of qubits when using PauliTerm.pauli_string",
                            DeprecationWarning)
              qubits = self.get_qubits()
  
          return ''.join(self[q] for q in qubits)
docs: Return a string representation of this PauliTerm without its coefficient and with
          implicit qubit indices.
  
          If a list of qubits is provided, each character in the resulting string represents
          a Pauli operator on the corresponding qubit. If qubit indices are not provided as input,
          the returned string will be all non-identity operators in the order. This doesn't make
          much sense, so please provide a list of qubits. Not providing a list of qubits is
          deprecated.
  
          >>> p = PauliTerm("X", 0) * PauliTerm("Y", 1, 1.j)
          >>> p.pauli_string()
          "XY"
          >>> p.pauli_string(qubits=[0])
          "X"
          >>> p.pauli_string(qubits=[0, 2])
          "XI"
  
          :param list qubits: The list of qubits to represent, given as ints. If None, defaults to
              all qubits in this PauliTerm.
          :return: The string representation of this PauliTerm, sans coefficient