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 = hoursself.__seconds = secondsself.__minutes = minutesself.__hours = hoursdef set(self,hours, minutes, seconds=0): self.__minutes = minutes""" Time will be advanced by one second """self.__seconds = seconds def tick(self): if self.__seconds == 59:self.__hours = 0 if self.__hours==23 else self.__hours + 1self.__seconds = 0 if (self.__minutes == 59): self.__minutes = 0def display(self):else: self.__minutes += 1; else: self.__seconds += 1;return "%2d:%2d:%2d" % (self.__hours, self.__minutes, self.__seconds)print("%d:%d:%d" % (self.__hours, self.__minutes, self.__seconds)) def __str__(self): 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)self.__day = daydef __init__(self, day=1, month=1, year=1900):self.__year = yearself.__month = month def leapyear(self,y): if y % 4:return 1;# not a leap year return 0; else: if y % 100:return 1;else: if y % 400: return 0 else:self.__year = yeardef set(self, day, month, year): self.__day = day self.__month = month def get():max_days = months[self.__month-1]return (self, self.__day, self.__month, self.__year) def advance(self): months = Calendar.months if self.__month == 2:self.__month = 1max_days += self.leapyear(self.__year) if self.__day == max_days: self.__day = 1 if (self.__month == 12): self.__year += 1if __name__ == "__main__":else: self.__month += 1 else: self.__day += 1 def __str__(self): return str(self.__day)+"/"+ str(self.__month)+ "/"+ str(self.__year)print(x)x = Calendar() print(x)x.advance()
The Calendar-Clock Class
from clock import Clockfrom calendar import Calendarclass CalendarClock(Clock, Calendar):def __init__(self, day,month,year,hours=0, minutes=0,seconds=0):Calendar.__init__(self, day, month, year)def __str__(self):Clock.__init__(self, hours, minutes, seconds)x = CalendarClock(24,12,57)return Calendar.__str__(self) + ", " + Clock.__str__(self) if __name__ == "__main__": print(x)print(x)for i in range(1000): x.tick() for i in range(1000):x.advance()
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