def blob_name(i):
    """
    Implements legacy schema for blobs naming:
        0-th blob is called 'weights'
        1-th blob is called 'biases'
    then, next blobs are called according to the new default schema
    with 'custom_' prefix: custom_2, custom_3 and so on.
    """
    predefined_names = ['weights', 'biases']
    if i < len(predefined_names):
        return predefined_names[i]
    else:
        return 'custom_{}'.format(i)