'map' object is not subscriptable

> /home/zbp/Linux/tjj/SPReID/main.py(145)Train()
144 ipdb.set_trace()
--> 145 tmp1 = batch_tuple_indx[iterk]
146 tmp2 = batch_tuples[dataset][batch_tuple_indx[iterk]]

ipdb> c
Exception in thread prefetch_loop:
multiprocessing.pool.RemoteTraceback:
"""
Traceback (most recent call last):
File "/home/zbp/anaconda3/lib/python3.6/multiprocessing/pool.py", line 119, in worker
result = (True, func(*args, **kwds))
File "/home/zbp/anaconda3/lib/python3.6/multiprocessing/pool.py", line 44, in mapstar
return list(map(*args))
File "/home/zbp/anaconda3/lib/python3.6/site-packages/chainer/iterators/multiprocess_iterator.py", line 428, in _fetch_run
data = _fetch_dataset[index]
File "/home/zbp/anaconda3/lib/python3.6/site-packages/chainer/dataset/dataset_mixin.py", line 67, in __getitem__
return self.get_example(index)
File "/home/zbp/Linux/tjj/SPReID/datachef.py", line 32, in get_example
fy = float(self.image_size[0]) / float(input_image.shape[0]) # Height
TypeError: 'map' object is not subscriptable
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/home/zbp/anaconda3/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/home/zbp/anaconda3/lib/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/home/zbp/anaconda3/lib/python3.6/site-packages/chainer/iterators/multiprocess_iterator.py", line 336, in _run
alive = self._task()
File "/home/zbp/anaconda3/lib/python3.6/site-packages/chainer/iterators/multiprocess_iterator.py", line 355, in _task
data_all = future.get(_response_time)
File "/home/zbp/anaconda3/lib/python3.6/multiprocessing/pool.py", line 644, in get
raise self._value
TypeError: 'map' object is not subscriptable

Even I use x = self.pool.apply((x,))[0],it doesn't solve the problem.
Thank you.