如何用python创建一个幻灯片大小比例为16:9的ppt文件

from pptx import Presentation
prs = Presentation()
title_slide_layout = prs.slide_layouts[1]
slide = prs.slides.add_slide(title_slide_layout)
title = slide.shapes.title
subtitle = slide.placeholders[1]

title.text = "Hello, World!"
subtitle.text = "python-pptx was here!"

prs.save('test.pptx')

我用上面的方式创建出来的幻灯片大小比例始终都为4:3，如何才能将大小改为16:9呢？