docs: def set_walltime(self, walltime):
          """
          Setting a walltime for the job
  
          >>> job.set_walltime(datetime.timedelta(hours=2, minutes=30))
  
          :param walltime: Walltime of the job (an instance of timedelta)
          :returns: self
          :rtype: self
          """
          if not isinstance(walltime, timedelta):
              raise TypeError(
                  'walltime must be an instance of datetime.timedelta. %s given' %
                  type(walltime)
              )
  
          self._options['walltime'] = walltime
          return self