$ python shallownet_animals.py --dataset ../datasets/animals/
 Using TensorFlow backend.
 [INFO] loading images...
 Traceback (most recent call last):
   File "shallownet_animals.py", line 35, in <module>
     (data, labels) = sdl.load(imagePaths, verbose=500)
  File "/home/swartz/dev/dl4cv/SB_Code/chapter12-first_cnn/pyimagesearch/datasets/simpledatasetloader.py", line 34, in load
     image = p.preprocess(image)
  File "/home/swartz/dev/dl4cv/SB_Code/chapter12-first_cnn/pyimagesearch/preprocessing/imagetoarraypreprocessor.py", line 12, in preprocess
     return img_to_array(image, data_format=self.dataFormat)
  File "/usr/lib/python2.7/dist-packages/keras_preprocessing/image/utils.py", line 278, in img_to_array
     raise ValueError('Unknown data_format: %s' % data_format)
ValueError: Unknown data_format: None

class ImageToArrayPreprocessor:
     def __init__(self, dataFormat=None):
         # store the image data format
         self.dataFormat = dataFormat