more conciser sampler

[bnu-wangxun]

https://github.com/michuanhaohao/reid-strong-baseline/blob/master/data/samplers/triplet_sampler.py

            batch_idxs = []
            for idx in idxs:
                batch_idxs.append(idx)
                if len(batch_idxs) == self.num_instances:
                    batch_idxs_dict[pid].append(batch_idxs)
                    batch_idxs = []

can be replaced with

batch_idxs_dict[label] = [idxs[i*self.num_instances : (i+1)*self.num_instances] for i in range(len(idxs)//self.num_instances)]

which is more concise and easier to understand!

[michuanhaohao]

Thank you very much. If you have check the code, you can commit a PR and become a contributor for this project.

[onlinehuazai]

  batch_idxs = batch_idxs_dict[pid].pop(0)

IndexError: pop from empty list