code: def flatten_comments(comments, root_level=0):
          stack = comments[:]
          for item in stack:
              item.nested_level = root_level
          retval, parent_candidates = [], {}
          while stack:
              item = stack.pop(0)
              if isinstance(item, praw.objects.MoreComments) and item.count == 0:
                  continue
              if item.parent_id:
                  parent = parent_candidates.get(item.parent_id[3:])
                  if parent:
                      item.nested_level = parent.nested_level + 1
              if hasattr(item, 'replies'):
                  for n in item.replies:
                      n.nested_level = item.nested_level + 1
                  stack[0:0] = item.replies
              parent_candidates[item.id] = item
              retval.append(item)
          return retval