docs: def define_options(default_conf):
      """
      Define the options from default.conf dynamically
      """
      default = {}
      with open(default_conf, 'rb') as f:
          exec_in(native_str(f.read()), {}, default)
  
      for name, value in default.iteritems():
          # if the option is already defined by tornado
          # override the value
          # a list of options set by tornado:
          # log_file_num_backups, logging, help,
          # log_to_stderr, log_file_max_size, log_file_prefix
          if name in options:
              setattr(options, name, value)
          # otherwise define the option
          else:
              define(name, value)