django return extra fields for model without storing in db code example

Example: django __str__ self multiple

class MyclubUser(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    email = models.EmailField('User Email')

    def __str__(self):
        return self.first_name + " " + self.last_name


class Subscriber(MyclubUser):
    date_joined = models.DateTimeField()