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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def save(self, *args, **kwargs):
 """ Save the created_by and last_modified_by fields based on the current admin user. """

        if not self.instance.id:
            self.instance.created_by = self.user
        self.instance.last_modified_by = self.user
        return super(ChangeableContentForm, self).save(*args, **kwargs)