old_contents: 
  class FieldBase(object):
      """Base class for all field types"""
  
      def __init__(self, source=None):
          self.source = source
  
      def populate(self, data):
          """Set the value or values wrapped by this field"""
          self.data = data
  
  class CharField(FieldBase):
      """Class to represent a simple string field"""
  
      def to_python(self):
          if self.data is None:
              return ''
          return unicode(self.data)
  
  class IntegerField(FieldBase):
  
      def to_python(self):
          return int(self.data)
  
new_contents: 
  class FieldBase(object):
      """Base class for all field types"""
  
      def __init__(self, source=None):
          self.source = source
  
      def populate(self, data):
          """Set the value or values wrapped by this field"""
          self.data = data
  
  class CharField(FieldBase):
  
      def to_python(self):
          if self.data is None:
              return ''
          return unicode(self.data)
  
  class IntegerField(FieldBase):
  
      def to_python(self):
          return int(self.data)
  
subject: Remove useless comment