code: def doc_open():
      
      doc_index = os.path.join(DOCS_DIRECTORY, 'build', 'html', 'index.html')
      if sys.platform == 'darwin':
          # Mac OS X
          subprocess.check_call(['open', doc_index])
      elif sys.platform == 'win32':
          # Windows
          subprocess.check_call(['start', doc_index], shell=True)
      elif sys.platform == 'linux2':
          # All freedesktop-compatible desktops
          subprocess.check_call(['xdg-open', doc_index])
      else:
          print_failure_message(
              "Unsupported platform. Please open `{0}' manually.".format(
                  doc_index))
docs: Build the HTML docs and open them in a web browser.