## Inheritance Example

### Introduction There aren't many good examples on inheritance available on the web. They are either extremely simple and artificial or they are way too complicated. We want to close the gap by providing an example which is on the one hand more realistic - but still not realistic - and on the other hand simple enough to see and understand the basic aspects of inheritance. In our previous chapter, we introduced inheritance formally.

To this purpose we define two base classes: One is an implementation of a clock and the other one of a calendar. Based on these two classes, we define a class CalendarClock, which inherits both from the class Calendar and from the class Clock.

### The Clock Class

class Clock(object):

def __init__(self,hours=0, minutes=0, seconds=0):
self.__hours = hours
self.__minutes = minutes
self.__seconds = seconds

def set(self,hours, minutes, seconds=0):
self.__hours = hours
self.__minutes = minutes
self.__seconds = seconds

def tick(self):
""" Time will be advanced by one second """
if self.__seconds == 59:
self.__seconds = 0
if (self.__minutes == 59):
self.__minutes = 0
self.__hours = 0 if self.__hours==23  else self.__hours + 1
else:
self.__minutes += 1;
else:
self.__seconds += 1;

def display(self):
print("%d:%d:%d" % (self.__hours, self.__minutes, self.__seconds))

def __str__(self):
return "%2d:%2d:%2d" % (self.__hours, self.__minutes, self.__seconds)

x = Clock()
print(x)
for i in range(10000):
x.tick()
print(x)


### The Calendar Class

class Calendar(object):
months = (31,28,31,30,31,30,31,31,30,31,30,31)

def __init__(self, day=1, month=1, year=1900):
self.__day = day
self.__month = month
self.__year = year

def leapyear(self,y):
if y % 4:
# not a leap year
return 0;
else:
if y % 100:
return 1;
else:
if y % 400:
return 0
else:
return 1;

def set(self, day, month, year):
self.__day = day
self.__month = month
self.__year = year

def get():
return (self, self.__day, self.__month, self.__year)
months = Calendar.months
max_days = months[self.__month-1]
if self.__month == 2:
max_days += self.leapyear(self.__year)
if self.__day == max_days:
self.__day = 1
if (self.__month == 12):
self.__month = 1
self.__year += 1
else:
self.__month += 1
else:
self.__day += 1

def __str__(self):
return str(self.__day)+"/"+ str(self.__month)+ "/"+ str(self.__year)

if __name__ == "__main__":
x = Calendar()
print(x)
print(x)


### The Calendar-Clock Class

from clock import Clock
from calendar import Calendar

class CalendarClock(Clock, Calendar):

def __init__(self, day,month,year,hours=0, minutes=0,seconds=0):
Calendar.__init__(self, day, month, year)
Clock.__init__(self, hours, minutes, seconds)

def __str__(self):
return Calendar.__str__(self) + ", " + Clock.__str__(self)

if __name__  == "__main__":
x = CalendarClock(24,12,57)
print(x)
for i in range(1000):
x.tick()
for i in range(1000):