python,hdf5,pytables,h5py,hdf5storage

It appears that this is not possible because it is expressly forbidden in the specification.

python,matlab,hdf5,hdf5storage

You are creating new data, then writing that new data to a file. That overwrites the file. You need to load the original .mat file, append to it, then save again. import hdf5storage import numpy as np matcontent = hdf5storage.loadmat('data.mat') matcontent[u'some_numbers'] = np.array([10, 50, 20]) hdf5storage.savemat('data.mat', matcontent) Then in Matlab...