old_contents: from django.db import models
  
  
  class Attachment(models.Model):
      file_name = models.FileField(upload_to='attachments')
  
      def __unicode__(self):
          return self.file_name
  
new_contents: from django.db import models
  
  from datetime import datetime
  
  
  class Attachment(models.Model):
      file_name = models.FileField(upload_to='attachments')
  
      def __unicode__(self):
          return unicode(self.file_name)
  
subject: Fix attachment representation