old_contents: from __future__ import absolute_import
  
  
  class Field(object):
      def __call__(self, val):
          return val
  
  
  class Numeric(Field):
      def __call__(self, val):
          return str(val)
  
new_contents: from __future__ import absolute_import
  
  
  class Field(object):
      def __call__(self, val):
          return val
  
  
  class Numeric(Field):
      def __call__(self, val):
          return int(val)
  
subject: fix numeric field