qiskit/quantum_info/operators/quaternion.py
def to_zyz(self):
        """Converts a unit-length quaternion to a sequence
        of ZYZ Euler angles.

        Returns:
            ndarray: Array of Euler angles.
        """
        mat = self.to_matrix()
        euler = np.zeros(3, dtype=float)
        if mat[2, 2] < 1:
            if mat[2, 2] > -1:
                euler[0] = math.atan2(mat[1, 2], mat[0, 2])
                euler[1] = math.acos(mat[2, 2])
                euler[2] = math.atan2(mat[2, 1], -mat[2, 0])
            else:
                euler[0] = -math.atan2(mat[1, 0], mat[1, 1])
                euler[1] = np.pi
        else:
            euler[0] = math.atan2(mat[1, 0], mat[1, 1])
        return euler
def to_zyz(self):
        """Converts a unit-length quaternion to a sequence
        of ZYZ Euler angles.

        Returns:
            ndarray: Array of Euler angles.
        """
        mat = self.to_matrix()
        euler = np.zeros(3, dtype=float)
        if mat[2, 2] < 1:
            if mat[2, 2] > -1:
                euler[0] = math.atan2(mat[1, 2], mat[0, 2])
                euler[1] = math.acos(mat[2, 2])
                euler[2] = math.atan2(mat[2, 1], -mat[2, 0])
            else:
                euler[0] = -math.atan2(mat[1, 0], mat[1, 1])
                euler[1] = np.pi
        else:
            euler[0] = math.atan2(mat[1, 0], mat[1, 1])
        return euler
Converts a unit-length quaternion to a sequence
        of ZYZ Euler angles.

        Returns:
            ndarray: Array of Euler angles.