Return zero-based index of *slide_layout* in this collection.

        Raises ValueError if *slide_layout* is not present in this collection.

def index(self, slide_layout):
        """Return zero-based index of *slide_layout* in this collection.

        Raises ValueError if *slide_layout* is not present in this collection.
        """
        for idx, this_layout in enumerate(self):
            if slide_layout == this_layout:
                return idx
        raise ValueError("layout not in this SlideLayouts collection")