Учет телефонных переговоров Python

#!/usr/bin/env python
 
from datetime import date, time
 
 
class Subscriber(object):
    def __init__(self, number, inn, address):
        self.number = number
        self.inn = inn
        self.address = address
 
    def print_subs(self):
        print self.number, self.inn, self.address
 
 
class City(object):
    def __init__(self, name, d_tariff, n_tariff):
        self.name = name
        self.d_tariff = d_tariff
        self.n_tariff = n_tariff
 
    def print_city(self):
        print self.name, self.d_tariff, self.n_tariff
 
 
class Call(object):
    def __init__(self, subscriber, city, calldate, minutes, calltime):
        self.subscriber = subscriber
        self.city = city
        self.calldate = calldate
        self.minutes = minutes
        self.calltime = calltime
 
    def print_call(self):
        print self.subscriber.number, self.city.name, self.calldate, self.minutes, self.calltime
 
sub1 = Subscriber('8675309', 12345, 'strname')
sub1.print_subs()
 
city1 = City('city1', 100, 50)
city1.print_city()
 
call1 = Call(sub1, city1, date(2005, 7, 14), 30, time(12, 30))
call1.print_call()