feature: reorder a slide

In order to repurpose an existing presentation As a developer using python-pptx I need the ability to change the ordering of slides in a deck

Candidate protocol:

>>> slides = prs.slides
>>> len(slides)
6
>>> slide = slides[2]
>>> slides.index(slide)
2
>>> slide.move_to(5)
>>> slides.index(slide)
5

[blaze33]

The following works fine for me:

def move_slide(self, presentation, old_index, new_index):
        xml_slides = presentation.slides._sldIdLst  # pylint: disable=W0212
        slides = list(xml_slides)
        xml_slides.remove(slides[old_index])
        xml_slides.insert(new_index, slides[old_index])

def delete_slide(self, presentation,  index):
        xml_slides = presentation.slides._sldIdLst  # pylint: disable=W0212
        slides = list(xml_slides)
        xml_slides.remove(slides[index])

[Amazinzay]

Because you’re working with lxml.etree._Element objects there, the code can be a little simpler:

def move_slide(slides, slide, new_idx):
    slides._sldIdLst.insert(new_idx, slide._element)

The basic insight here is that lxml does not make copies unless you tell it to. If you stick an element somewhere else, it comes out of wherever it was before.

I can’t think of any edge cases off the top of my head. This is the approach I would use if I was doing it myself.

I was able to get this working with a slight modification.

def move_slide(slides, slide, new_idx):
        slides._sldIdLst.insert(new_idx, slides._sldIdLst[slides.index(slide)])

The slide element is not what is being moved, but rather the sldId Element.