code: def command(self, command, value=1, check=True, allowable_errors=None,
                  codec_options=DEFAULT_CODEC_OPTIONS, _deadline=None, **kwargs):
          
          if isinstance(command, (bytes, unicode)):
              command = SON([(command, value)])
          options = kwargs.copy()
          command.update(options)
  
          def on_ok(response):
              if check:
                  msg = "TxMongo: command {0} on namespace {1} failed with '%s'".format(repr(command), ns)
                  _check_command_response(response, msg, allowable_errors)
  
              return response
  
          ns = self["$cmd"].with_options(codec_options=codec_options)
          return ns.find_one(command, _deadline=_deadline).addCallback(on_ok)
docs: command(command, value=1, check=True, allowable_errors=None, codec_options=DEFAULT_CODEC_OPTIONS)