code: def slice_vec(expr, start, stop):
      
      weld_obj = WeldObject(encoder_, decoder_)
  
      expr_var = weld_obj.update(expr)
      if isinstance(expr, WeldObject):
          expr_var = expr.obj_id
          weld_obj.dependencies[expr_var] = expr
  
      weld_template = """
      slice(%(expr)s, %(start)sL, %(stop)sL)
      """
      weld_obj.weld_code = weld_template % {"expr":expr_var,
                                            "start":start,
                                            "stop":stop}
      return weld_obj
docs: Slices the vector.
  
      Args:
        expr (WeldObject)
        start (Long)
        stop (Long)