title: PyTorch - Torchvision - BrokenPipeError: [Errno 32] Broken pipe
body: <p>I'm trying to carry out the tutorial named <a href="https://pytorch.org/tutorials/beginner/blitz/cifar10_tutorial.html#sphx-glr-beginner-blitz-cifar10-tutorial-py" rel="noreferrer">"Training a classifier"</a> with PyTorch.
  WHen trying to debug this part of the code : </p>
  
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  
  # functions to show an image
  
  
  def imshow(img):
      img = img / 2 + 0.5     # unnormalize
      npimg = img.numpy()
      plt.imshow(np.transpose(npimg, (1, 2, 0)))
  
  
  # get some random training images
  dataiter = iter(trainloader)
  images, labels = dataiter.next()
  
  # show images
  imshow(torchvision.utils.make_grid(images))
  # print labels
  print(' '.join('%5s' % classes[labels[j]] for j in range(4)))
  </code></pre>
  
  <p>I get this error message :</p>
  
  <pre><code>Files already downloaded and verified Files already downloaded and verified 
  Files already downloaded and verified Files already downloaded and verified Traceback (most recent call last):   
  File "&lt;string&gt;", line 1, in &lt;module&gt;   
  File "D:\Anaconda\lib\multiprocessing\spawn.py", line 105, in spawn_main
      exitcode = _main(fd)   
  File "D:\Anaconda\lib\multiprocessing\spawn.py", line 114, in _main
      prepare(preparation_data)   
  File "D:\Anaconda\lib\multiprocessing\spawn.py", line 225, in prepare
      _fixup_main_from_path(data['init_main_from_path'])   
  File "D:\Anaconda\lib\multiprocessing\spawn.py", line 277, in
  _fixup_main_from_path
      run_name="__mp_main__")   
  File "D:\Anaconda\lib\runpy.py", line 263, in run_path
      pkg_name=pkg_name, script_name=fname)   
  File "D:\Anaconda\lib\runpy.py", line 96, in _run_module_code
      mod_name, mod_spec, pkg_name, script_name)   
  File "D:\Anaconda\lib\runpy.py", line 85, in _run_code
      exec(code, run_globals)   
  File "d:\Yggdrasil\Programmation\PyTorch\TutorialCIFAR10.py", line 36, in &lt;module&gt;
      dataiter = iter(trainloader)   
  File "D:\Anaconda\lib\site-packages\torch\utils\data\dataloader.py", line 451, in __iter__
      return _DataLoaderIter(self)   
  File "D:\Anaconda\lib\site-packages\torch\utils\data\dataloader.py", line 239, in __init__
      w.start()   
  File "D:\Anaconda\lib\multiprocessing\process.py", line 105, in start
      self._popen = self._Popen(self)   
  File "D:\Anaconda\lib\multiprocessing\context.py", line 223, in _Popen
      return _default_context.get_context().Process._Popen(process_obj)     
  File "D:\Anaconda\lib\multiprocessing\context.py", line 322, in _Popen
      return Popen(process_obj)   
  File "D:\Anaconda\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
      prep_data = spawn.get_preparation_data(process_obj._name)   
  File "D:\Anaconda\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
      _check_not_importing_main()   
  File "D:\Anaconda\lib\multiprocessing\spawn.py", line 136, in
  _check_not_importing_main
      is not going to be frozen to produce an executable.) 
  RuntimeError:
          An attempt has been made to start a new process before the
          current process has finished its bootstrapping phase.
  
          This probably means that you are not using fork to start your
          child processes and you have forgotten to use the proper idiom
          in the main module:
  
              if __name__ == '__main__':
                  freeze_support()
                  ...
  
          The "freeze_support()" line can be omitted if the program
          is not going to be frozen to produce an executable. 
   Traceback (most recent call last):   
   File "d:\Yggdrasil\Programmation\PyTorch\TutorialCIFAR10.py", line 36, in &lt;module&gt;
      dataiter = iter(trainloader)   
   File "D:\Anaconda\lib\site-packages\torch\utils\data\dataloader.py", line 451, in __iter__
      return _DataLoaderIter(self)   
   File "D:\Anaconda\lib\site-packages\torch\utils\data\dataloader.py", line 239, in __init__
      w.start()   
   File "D:\Anaconda\lib\multiprocessing\process.py", line 105, in start
      self._popen = self._Popen(self)   
   File "D:\Anaconda\lib\multiprocessing\context.py", line 223, in _Popen
      return _default_context.get_context().Process._Popen(process_obj)   File "D:\Anaconda\lib\multiprocessing\context.py", line 322, in _Popen
      return Popen(process_obj)   
   File "D:\Anaconda\lib\multiprocessing\popen_spawn_win32.py", line 65, in
  __init__
      reduction.dump(process_obj, to_child)   
   File "D:\Anaconda\lib\multiprocessing\reduction.py", line 60, in dump
      ForkingPickler(file, protocol).dump(obj) 
   BrokenPipeError: [Errno 32] Broken pipe
  </code></pre>
  
  <p>All the previous lines in the tutorial are working perfectly.</p>
  
  <p>Does someone know how to solve this, please ?
  Thanks a lot in advance</p>