models.py

from django.db import models

from django.contrib.auth.models import User
from django.db import models, transaction

class Account(models.Model):
    balance = models.IntegerField(default=0)
    user = models.ForeignKey(User)
    
    def deposit(self, amount):
        self.balance += amount
        self.save()
    
    def withdraw(self, amount):
        if amount > self.balance:
            raise errors.InsufficientFunds()
        self.balance -= amount
        self.save()