code: def calculate_sqnr(expected, actual):
      noise = expected - actual
  
      def power_sum(xs):
          return sum([x * x for x in xs])
  
      signal_power_sum = power_sum(expected)
      noise_power_sum = power_sum(noise)
      return signal_power_sum / (noise_power_sum + 1e-15)
  
imports: import argparse
  import sys
  import os
  import os.path
  import numpy
  import six
  import common
label_desc: Use image node_id 2 for calling a global function with example usage: calculate_sqnr(expected, actual) and returns: unknown, sum