The variable mean_data is a nested list, in Python accessing a nested list cannot be done by multi-dimensional slicing, i.e.: mean_data[1,2], instead one would write mean_data[1][2].
This is becausemean_data[2] is a list. Further indexing is done recursively – since mean_data[2] is a list, mean_data[2][0] is the first index of that list.
Additionally, mean_data[:][0] does not work because mean_data[:] returns mean_data.
The solution is to replace the array ,or import the original data, as follows:
mean_data = np.array(mean_data)
numpy arrays (like MATLAB arrays and unlike nested lists) support multi-dimensional slicing with tuples.