def snapPath(basePath, snapNum, chunkNum=0):
    """ Return absolute path to a snapshot HDF5 file (modify as needed). """
    snapPath = basePath + '/snapdir_' + str(snapNum).zfill(3) + '/'
    filePath = snapPath + 'snap_' + str(snapNum).zfill(3)
    filePath += '.' + str(chunkNum) + '.hdf5'
    return filePath