Update iou_neg_piecewise_sampler.py (open-mmlab#2017)

fix lint

mmdet3d/models/task_modules/samplers/iou_neg_piecewise_sampler.py

@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+import math
+
 import torch
 
 from mmdet3d.registry import TASK_UTILS
@@ -74,9 +76,11 @@ def _sample_neg(self, assign_result, num_expected, **kwargs):
  # if the numbers of negative samplers in previous
  # pieces are less than the expected number, extend
  # the same number in the current piece.
- piece_expected_num = int(
- num_expected *
- self.neg_piece_fractions[piece_inds]) + extend_num
+ piece_expected_num = min(
+ num_expected,
+ math.ceil(num_expected *
+ self.neg_piece_fractions[piece_inds]) +
+ extend_num)
  min_iou_thr = self.neg_iou_thr[piece_inds + 1]
  max_iou_thr = self.neg_iou_thr[piece_inds]
  piece_neg_inds = torch.nonzero(