old_contents: import numpy as np
  
  import constants
  
  def mean_normalize(entry):
      """
      Mean normalizes a pixel vector. Entry is a numpy array of unrolled pixel vectors with
      two side by side facial images for each entry.
      """
      entry -= np.mean(entry, axis=0)
      return entry
  
  def get_key(idx):
      """
      Each image pair is a top level key with a keyname like 00059999, in increasing
      order starting from 00000000.
      """
      return "%08d" % (idx,)
  
new_contents: import numpy as np
  
  import constants
  
  def mean_normalize(entry):
      """
      Mean normalizes a pixel vector. Entry is a numpy array of unrolled pixel vectors with
      two side by side facial images for each entry.
      """
      entry -= np.mean(entry, axis=0)
      return entry
  
  def get_key(idx):
      """
      Each image pair is a top level key with a keyname like 00000059999, in increasing
      order starting from 00000000000.
      """
      return "%011d" % (idx,)
  
subject: Increase key length for larger datasets.