I have two lists of data points:
list_x = [-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
Because your data is approximate (i.e., it has been quantized), you want an approximating spline, not an interpolating spline.