title: Placeholder for pictures in python-pptx
body: <p>I want to make a presentation with python-pptx with 3 pictures in a row on each slide.</p>
  
  <pre><code>from pptx import Presentation
  from pptx.util import Inches
  
  height = Inches(3) #size  
  top = Inches(0)  #y-position
  
  img = 'image001.png'
  
  prs = Presentation() #create presentation
  blank_slide_layout = prs.slide_layouts[6] #define side layout
  
  
  for j in range(0,5):
      slide = prs.slides.add_slide(blank_slide_layout) #add slide
      left = Inches(0) #x-position
      for i in range(0,3):
          pic = slide.shapes.add_picture(img, left, top, height=height)
          left = left+height    
  
  prs.save('test.pptx')
  
  </code></pre>
  
  <p>This here is working but i want to understand the placeholders.
  I need first to fill the first (left) picture at each slide and jump back to the first slide and all second (mid) pictures and the same for the third column because i am loading the pics from a txt-file.</p>
  
  <p>The txt file look like</p>
  
  <pre><code>pic1a
  pic2a
  pic3a
  pic1b
  pic2b
  ...
  </code></pre>
  
  <p>and i need the pics in the presentation like</p>
  
  <pre><code>pic1a pic1b pic1c
  pic2a..
  pic3a...
  </code></pre>
  
  <p>How can i add placeholders and jump to them.
  The manual is not helping me.</p>