Is there a way to add a textbox to a layout?

prs = Presentation("filename.pptx")
for layout in prs.slide_layouts:
        textbox = layout.shapes.add_textbox()

Gives me AttributeError: 'LayoutShapes' object has no attribute 'add_textbox'. I see that this method is available in _BaseGroupShapes but the LayoutShapes class inherits directly from _BaseShapes.

Thanks :)