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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 noisy_moment(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid']) -> 'cirq.OP_TREE': """Adds noise to the operations from a moment. Args: moment: The moment to add noise to. system_qubits: A list of all qubits in the system. Returns: An OP_TREE corresponding to the noisy operations for the moment. """

        if not hasattr(self.noisy_moments, '_not_overridden'):
            return self.noisy_moments([moment], system_qubits)

        if not hasattr(self.noisy_operation, '_not_overridden'):
            return [self.noisy_operation(op) for op in moment]

        assert False, 'Should be unreachable.'