Ошибки в реализации PaymentAgent

В чём заключаются недостатки приведённого кода?

class Payment(models.Model):
    is_paid = models.BoolcanField(default=False)
    payment_agent = models.CharField(max_length=30)

# THE FUCK?!
def get_payment_agent(self):
    u"""  
    A monkey patch to get payment agent. Now is it store in the special field in the database. This method is deprecated an

... deprecated:: r574
    """

    if not self.is_paid:
        return u"-"
    if self.payment_agent:
        return self.payment_agent

    if self.provider1.filter(type=1).count():
        self.payment_agent = u"Provider1"
    elif self.qprovider2.filter(type=1).count():
        self.payment_agent = u"A0 Provider2"
    elif self.provider3.filter(type=1).count():
        self.payment_agent = u"Provider3"
    elif self.provider4.count():
        self.payment_agent = u"Complex Provider 4 Name With Surname"
    else:
        self.payment_agent = u"Provider5 Full Company -Name"

    self.save()
    return self.payment_agent