code: def _get_available_extensions():
      
      extensions = []
  
      # from filenames
      parsers_dir = os.path.join(os.path.dirname(__file__))
      glob_filename = os.path.join(parsers_dir, "*" + _FILENAME_SUFFIX + ".py")
      ext_re = re.compile(glob_filename.replace('*', "(?P<ext>\w+)"))
      for filename in glob.glob(glob_filename):
          ext_match = ext_re.match(filename)
          ext = ext_match.groups()[0]
          extensions.append(ext)
          extensions.append('.' + ext)
  
      # from relevant synonyms (don't use the '' synonym)
      for ext in EXTENSION_SYNONYMS.keys():
          if ext:
              extensions.append(ext)
              extensions.append(ext.replace('.', '', 1))
      extensions.sort()
      return extensions
docs: Get a list of available file extensions to make it easy for
      tab-completion and exception handling.