text: import subprocess
  import sys
  from sphinx.util.compat import Directive
  
  def setup(app):
      app.add_directive('yt_showfields', ShowFields)
      setup.app = app
      setup.config = app.config
      setup.confdir = app.confdir
      
      retdict = dict(
          version='1.0',
          parallel_read_safe=True,
          parallel_write_safe=True
      )
  
      return retdict
  
  class ShowFields(Directive):
      required_arguments = 0
      optional_arguments = 0
      parallel_read_safe = True
      parallel_write_safe = True
  
      def run(self):
          rst_file = self.state_machine.document.attributes['source']
          lines = subprocess.check_output(
              [sys.executable, './helper_scripts/show_fields.py'])
          lines = lines.decode('utf8')
          lines = lines.split('\n')
          self.state_machine.insert_input(lines, rst_file)
          return []
  