title: Python cPickle: load fails with UnpicklingError
body: <p>I've made a pickle file using the following.</p>
  
  <pre><code>from PIL import Image
  import pickle
  import os
  import numpy
  import time
  
  trainpixels = numpy.empty([80000,6400])
  trainlabels = numpy.empty(80000)
  validpixels = numpy.empty([10000,6400])
  validlabels = numpy.empty(10000)
  testpixels = numpy.empty([10408,6400])
  testlabels = numpy.empty(10408)
  
  i=0
  tr=0
  va=0
  te=0
  for (root, dirs, filenames) in os.walk(indir1):
      print 'hello'
      for f in filenames:
              try:
                      im = Image.open(os.path.join(root,f))
                      Imv=im.load()
                      x,y=im.size
                      pixelv = numpy.empty(6400)
                      ind=0
                      for ii in range(x):
                              for j in range(y):
                                      temp=float(Imv[j,ii])
                                      temp=float(temp/255.0)
                                      pixelv[ind]=temp
                                      ind+=1
                      if i&lt;40000:
                              trainpixels[tr]=pixelv
                              tr+=1
                      elif i&lt;45000:
                              validpixels[va]=pixelv
                              va+=1
                      else:
                              testpixels[te]=pixelv
                              te+=1
                      print str(i)+'\t'+str(f)
                      i+=1
              except IOError:
                      continue
  trainimage=(trainpixels,trainlabels)
  validimage=(validpixels,validlabels)
  testimage=(testpixels,testlabels)
  
  output=open('data.pkl','wb')
  
  pickle.dump(trainimage,output)
  pickle.dump(validimage,output)
  pickle.dump(testimage,output)
  </code></pre>
  
  <p>Now I'm unpickling with load_data() function of the following code:
  <a href="http://www.deeplearning.net/tutorial/code/logistic_sgd.py" rel="nofollow">http://www.deeplearning.net/tutorial/code/logistic_sgd.py</a>
  which is called by running
  <a href="http://www.deeplearning.net/tutorial/code/rbm.py" rel="nofollow">http://www.deeplearning.net/tutorial/code/rbm.py</a></p>
  
  <p>but it returns the following error.</p>
  
  <pre><code>cPickle.UnpicklingError: A load persistent id instruction was encountered,
  but no persistent_load function was specified.
  </code></pre>
  
  <p>It seems like data structure is unmatched, but I can' figure out how it should be..</p>
  
  <p>For reference, the size of the pickle file is over 16GB, with its gzip over 1GB</p>