'Create a snapshot of the invoice transaction.
The returned dictionary is JSON-serializable.
Returns:
dict'

def snapshot(self):

    return {'amount': unicode(self.amount), 'currency': self.currency, 'comments': self.comments, 'status': self.status, 'created_by': self.created_by.username, 'last_modified_by': self.last_modified_by.username}
