djadhere/banking/models.py

from django.db import models
from django.core.validators import MaxValueValidator


class Payment(models.Model):
    TRANSFERT = 0 
    WITHDRAWAL = 1 
    PAYMENT_CHOICES = ( 
        (TRANSFERT, 'Virement'),
        (WITHDRAWAL, 'Prélèvement'),
    )   
    amount = models.DecimalField(max_digits=9, decimal_places=2, verbose_name='Montant')
    period = models.PositiveIntegerField(validators=[MaxValueValidator(12)], verbose_name='Période')
    payment_method = models.IntegerField(choices=PAYMENT_CHOICES, verbose_name='Méthode de paiement')

    class Meta:
        verbose_name = 'paiement'

    def __str__(self):
        s = str(self.amount) + '€' 
        if self.period:
            s += '%d/mois' % self.period
        if self.payment_method == self.TRANSFERT:
            s += ' (virement)'
        elif self.payment_method == self.WITHDRAWAL:
            s += ' (prélèvement)'
        return s