I’m using windows10 64-bit, python 3.7.3 in Jupyter Notebook(anaconda) environment, intel i9-7980XE:
When I try to enumerate over the DataLoader() object with num_workers > 0 like:
> if __name__=='__main__':
>     ...    
>     DL = DataLoader(data, batch_size=8, shuffle=True, num_workers=8)
>     for i in enumerate(DL ):
>         print(i)

I get the following error (also when using next(iter(DL )):
TypeError: can’t pickle odict_keys objects
Full Error:
TypeError                                 Traceback (most recent call last)
<ipython-input-19-ebb16a21aa89> in <module>
  ...
----> 6     for i in enumerate(DL ):
...

C:\ProgramData\Anaconda3\lib\site-packages\torch\utils\data\dataloader.py in __iter__(self)
    817 
    818     def __iter__(self):
--> 819         return _DataLoaderIter(self)
    820 
    821     def __len__(self):

C:\ProgramData\Anaconda3\lib\site-packages\torch\utils\data\dataloader.py in __init__(self, loader)
    558                 #     before it starts, and __del__ tries to join but will get:
    559                 #     AssertionError: can only join a started process.
--> 560                 w.start()
    561                 self.index_queues.append(index_queue)
    562                 self.workers.append(w)

C:\ProgramData\Anaconda3\lib\multiprocessing\process.py in start(self)
    110                'daemonic processes are not allowed to have children'
    111         _cleanup()
--> 112         self._popen = self._Popen(self)
    113         self._sentinel = self._popen.sentinel
    114         # Avoid a refcycle if the target function holds an indirect

C:\ProgramData\Anaconda3\lib\multiprocessing\context.py in _Popen(process_obj)
    221     @staticmethod
    222     def _Popen(process_obj):
--> 223         return _default_context.get_context().Process._Popen(process_obj)
    224 
    225 class DefaultContext(BaseContext):

C:\ProgramData\Anaconda3\lib\multiprocessing\context.py in _Popen(process_obj)
    320         def _Popen(process_obj):
    321             from .popen_spawn_win32 import Popen
--> 322             return Popen(process_obj)
    323 
    324     class SpawnContext(BaseContext):

C:\ProgramData\Anaconda3\lib\multiprocessing\popen_spawn_win32.py in __init__(self, process_obj)
     87             try:
     88                 reduction.dump(prep_data, to_child)
---> 89                 reduction.dump(process_obj, to_child)
     90             finally:
     91                 set_spawning_popen(None)

C:\ProgramData\Anaconda3\lib\multiprocessing\reduction.py in dump(obj, file, protocol)
     58 def dump(obj, file, protocol=None):
     59     '''Replacement for pickle.dump() using ForkingPickler.'''
---> 60     ForkingPickler(file, protocol).dump(obj)
     61 
     62 #

TypeError: can't pickle odict_keys objects