code: def get_placeholders(template_name):
      
      try:
          temp = loader.get_template(template_name)
      except TemplateDoesNotExist:
          return []
  
      plist, blist = [], []
      try:
          # django 1.8
          _placeholders_recursif(temp.template.nodelist, plist, blist)
      except AttributeError:
          # django 1.7
          # raise
          _placeholders_recursif(temp.nodelist, plist, blist)
      return plist
docs: Return a list of PlaceholderNode found in the given template.
  
      :param template_name: the name of the template file