Because dataset is a list

>>> dataset
[[1.658985, 4.285136], [-3.453687, 3.424321], [4.838138, -1.151539], [-5.379713, -3.362104], [0.972564, 2.924086], [-3.567919, 1.531611], [0.450614, -3.302219], [-3.487105, -1.724432], [2.668759, 1.594842], [-3.156485, 3.191137], [3.165506, -3.999838], [-2.786837, -3.099354], [4.208187, 2.984927], [-2.123337, 2.943366], [0.704199, -0.479481], [-0.39237, -3.963704], [2.831667, 1.574018], [-0.790153, 3.343144], [2.943496, -3.357075], [-3.195883, -2.283926], [2.336445, 2.875106], [-1.786345, 2.554248], [2.190101, -1.90602], [-3.403367, -2.778288], [1.778124, 3.880832], [-1.688346, 2.230267], [2.592976, -2.054368], [-4.007257, -3.207066], [2.257734, 3.387564], [-2.679011, 0.785119], [0.939512, -4.023563], [-3.674424, -2.261084], [2.046259, 2.735279], [-3.18947, 1.780269], [4.372646, -0.822248], [-2.579316, -3.497576], [1.889034, 5.1904], [-0.798747, 2

So this problem occurs when you get the first column

>>> dataset[:,0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers or slices, not tuple

It needs to be transformed into a matrix

>>> dataset=mat(dataset)
>>> dataset[:,0]
matrix([[ 1.658985],
        [-3.453687],
        [ 4.838138],
        [-5.379713],
        [ 0.972564],
        [-3.567919],
        [ 0.450614],
        [-3.487105],
        [ 2.668759],
        [-3.156485],
        [ 3.165506],