Thought I'd add the method definition here too <pre>def load_backend(self, presentation=None, filename=None):
</pre>

In case you weren't aware in python presentation=None and filename=None are keyword arguments. So in the calling functions to reach those arguments you could pass things this way:

<pre>
load_backend(presentation=some_presentation)
load_backend(filename=some_filename)
</pre>

If you don't pass keywords python assumes positional order is used.