code: def compute_mean(dataset):
      print("compute mean image")
      sum_image = 0
      N = len(dataset)
      for i, (image, _) in enumerate(dataset):
          sum_image += image
          sys.stderr.write("{} / {}\r".format(i, N))
          sys.stderr.flush()
      sys.stderr.write("\n")
      return sum_image / N
  
imports: import argparse
  import sys
  import numpy
  import chainer
label_desc: Use image node_id 1 for calling a global function with example usage: compute_mean(dataset) and returns: unknown