dateClass.py

import sys


class MyDate:
    '''
    MyDate: A simple implementation of date as a class.
    '''

    def __init__(self, day=1, month=1, year=2000):
        '''
        Objective: To initialize data members of object MyDate
        Input Parameters:
            self (implicit parameter) - object of type MyDate
            day, month, and year - int
        Return Value: None
        '''
        if not (type(day) == int and type(month) == int and
                        type(year) == int):
            print('Invalid data provided for date')
            sys.exit()
        if month > 0 and month <= 12:
            self.month = month
        else:
            print('Invalid value for month')
            sys.exit()
        if year > 1900:
            self.year = year
        else:
            print('Invalid value for year. Year should be greater\
            than 1900.')
            sys.exit()
        self.day = self.checkDay(day)  # validate day

    def checkDay(self, day):
        '''
        Objective: To validate day component
        Input Parameters:
            self (implicit parameter) - object of type MyDate
            day - numeric
        Return Value: day if it is correct else message 'Invalid
            value for the day' is printed and the program is terminated
        '''
        # currentYear: list of no of days in months of current year

        if self.year % 400 == 0 or (self.year % 100 != 0 and self.year % 4 == 0):  # if leap year
            currentYear = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
        else:
            currentYear = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
        if (day > 0 and day <= currentYear[self.month - 1]):
            return day
        else:
            print('Invalid value for day')
            sys.exit()

    def __str__(self):
        '''
        Objective: To return string representation of object
        Input Parameter:
            self (implicit parameter) - object of type MyDate
        Return Value: string
        '''
        # Approach: use dd-mm-yyyy format
        if self.day <= 9:
            day = '0' + str(self.day)
        else:
            day = str(self.day)
        if self.month <= 9:
            month = '0' + str(self.month)
        else:
            month = str(self.month)
        return day + '-' + month + '-' + str(self.year)

    def __eq__(self, other):
        '''
        Objective: To compare two MyDate objects for equality
        Input Parameters:
            self (implicit parameter) - object of type MyDate
            other - object of type MyDate
        Return Value: True if equal else False
        '''
        # check for equality of year, month, day
        if isinstance(other, MyDate):
            return (self.day == other.day) and (self.month == other.month) \
                                           and (self.year == other.year)
        else:
            print('Type Mismatch')
            sys.exit()

    def __lt__(self, other):
        '''
        Objective: To compare two MyDate objects
        Input Parameters:
            self (implicit parameter) - object of type MyDate
            other - object of type MyDate
        Return Value: True if value of first MyDate object is less
                      than seconds, else False
        '''
        # compare by year, month, day successively
        if isinstance(other, MyDate):
            if self.year < other.year:
                answer = True
            elif self.year == other.year and \
                            self.month < other.month:
                answer = True
            elif self.year == other.year and self.month == other.month \
                    and self.day < other.day:
                answer = True
            else:
                answer = False
            return answer
        else:
            print('Type Mismatch')
            sys.exit()


def main():
    '''
    Objective: To create objects of class Date and to perform operations on it
    Input Parameter: None
    Return Value: None
    '''
    today = MyDate(3, 9, 2014)
    print(today)
    defaultDate = MyDate()
    print(defaultDate)


if __name__ == '__main__':
    main()