[GitHub] firstdeathmaker commented on issue #8749: [FIX ATTACHED] Not working example on Iterators tutorial - SimpleIter

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firstdeathmaker commented on issue #8749: [FIX ATTACHED] Not working example on Iterators tutorial - SimpleIter
URL: https://github.com/apache/incubator-mxnet/issues/8749#issuecomment-352791952
 
 
   I found the error (if it only appears when you use Python 3.x instead of Python 2): The behaviour of the zip function of python was changed. In python 3, you get a one-time iterator. Therefore, you cannot reuse it. You can change the example code of SimpleIter this way to get it to work in Python 3 (it will create a new zip-iterator when calling the properties and uses a call to that property in next() intead of calling the internal one:
   
   `class SimpleIter(mx.io.DataIter):
       def __init__(self, data_names, data_shapes, data_gen,
                    label_names, label_shapes, label_gen, num_batches=10):
           self._data_names = data_names
           self._data_shapes = data_shapes
           self._label_names = label_names
           self._label_shapes = label_shapes
           self.num_batches = num_batches
           self.data_gen = data_gen
           self.label_gen = label_gen
           self.cur_batch = 0
   
       def __iter__(self):
           return self
   
       def reset(self):
           self.cur_batch = 0
   
       def __next__(self):
           return self.next()
   
       @property
       def provide_data(self):
           return zip(self._data_names, self._data_shapes)
   
       @property
       def provide_label(self):
           return zip(self._label_names, self._label_shapes)
   
       def next(self):
           if self.cur_batch < self.num_batches:
               self.cur_batch += 1
               data = [mx.nd.array(g(d[1])) for d,g in zip(self.provide_data, self.data_gen)]
               label = [mx.nd.array(g(d[1])) for d,g in zip(self.provide_label, self.label_gen)]
               return mx.io.DataBatch(data, label)
           else:
               raise StopIteration`

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