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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pauli_string(self, qubits=None):
 """ 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. "XY" "X" "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 """

        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)