I think @mtomwing previously suggested to combine this method with the above (though his comment seems to have disappeared).

E.g.
```python
def get_presentations_list(self, fname):
    self._open_file()  # Or just get rid of open_file() and put the code directly in this method.
    return ...
```

I think that would be nicer than adding an extra step when using the importer. E.g.

```python
importer.open_file(...)
importer.get_presentations_list()
```

Thoughts?