text: """
  Usage: cat pytorch_vision_vgg.md | python formatter.py | notedown >pytorch_vision_vgg.ipynb
  """
  import sys
  import yaml
  
  header = []
  markdown = []
  header_read = False
  with open('/dev/stdin', 'r') as input, open('/dev/stdout', 'w') as output:
      for line in input:
          if line.startswith('---'):
              header_read = not header_read
              continue
          if header_read == True:
              header += [line]
          else:
              markdown += [line]
  
      header = yaml.load(''.join(header), Loader=yaml.BaseLoader)
      if header is None:
          # This assumes the markdown document has a yaml header
          # but some documents, like the README.md do not
          # Don't bother rendering them
          exit()
  
      images = []
      try:
          if header['featured_image_1'] != 'no-image':
              images.append(header['featured_image_1'])
          if header['featured_image_2'] != 'no-image':
              images.append(header['featured_image_2'])
      except:
          pass
  
      pre = []
  
      if 'accelerator' in header.keys():
          acc = header['accelerator']
          if acc == 'cuda':
              note = ['### This notebook requires a GPU runtime to run.\n',
                      '### Please select the menu option "Runtime" -> "Change runtime type", select "Hardware Accelerator" -> "GPU" and click "SAVE"\n\n',
                      '----------------------------------------------------------------------\n\n']
              pre += note
          elif acc == 'cuda-optional':
              note = ['### This notebook is optionally accelerated with a GPU runtime.\n',
                      '### If you would like to use this acceleration, please select the menu option "Runtime" -> "Change runtime type", select "Hardware Accelerator" -> "GPU" and click "SAVE"\n\n',
                      '----------------------------------------------------------------------\n\n']
              pre += note
  
      pre += ['# ' + header['title'] + '\n\n']
      pre += ['*Author: ' + header['author'] + '*' + '\n\n']
      pre += ['**' + header['summary'] + '**' + '\n\n']
  
      if len(images) == 2:
          pre += ['_ | _\n']
          pre += ['- | -\n']
          pre += ['![alt](https://pytorch.org/assets/images/{}) | '
                  '![alt](https://pytorch.org/assets/images/{})\n\n'.format(*images)]
      elif len(images) == 1:
          pre += ['<img src="https://pytorch.org/assets/images/{}" alt="alt" width="50%"/>\n\n'.format(*images)]
  
      markdown = pre + markdown
      output.write(''.join(markdown))
  