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 to 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
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)
def advance(self):
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)
x.advance()
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):
x.advance()
print(x)