docs: def export_img(visio_filename, image_filename, pagenum=None, pagename=None):
      """ Exports images from visio file """
      # visio requires absolute path
      image_pathname = os.path.abspath(image_filename)
  
      if not os.path.isdir(os.path.dirname(image_pathname)):
          msg = 'Could not write image file: %s' % image_filename
          raise IOError(msg)
  
      with VisioFile.Open(visio_filename) as visio:
          pages = filter_pages(visio.pages, pagenum, pagename)
          try:
              if len(pages) == 1:
                  pages[0].Export(image_pathname)
              else:
                  digits = int(log(len(pages), 10)) + 1
                  basename, ext = os.path.splitext(image_pathname)
                  filename_format = "%s%%0%dd%s" % (basename, digits, ext)
  
                  for i, page in enumerate(pages):
                      filename = filename_format % (i + 1)
                      page.Export(filename)
          except Exception:
              raise IOError('Could not write image: %s' % image_pathname)