[SOLVED] CS515 Assignment 12-How to get a Date!

Grab the starting file date_template.py
Save your copy as date.py (and change Hw 11 to Hw 12 if you like).

Take a moment to look over this file as it stands so far…
Notice that in this Date class there are three attributes, also known as data members:

Note that self is used to denote any object value of class Date! Methods are just functions…

Object-oriented programming tends to have some of its own names for familiar things. For
example, method is the “OOP” name for function. In particular, a method is a function whose first input is self!

Note that the Date class has an __init__ method and a __str__ method. As we’ve discussed in class, Python expects to see these special methods in virtually every class. The double underscores before and after these method names indicate that these methods are special methods that Python knows to look for. In the case of __init__, this is the method that Python looks for when making a new Date object. In the case of __str__, this is the method that Python looks for when it needs

to represent the object as a string. Notice the line

s = ‘%02d/%02d/%04d’ % (self.month, self.day, self.year)

Traditionally, functions called by objects are called methods. There is no really good reason for this. They

are functions—the only thing special about them is that they are defined in a class and they are called

after a dot or period following the name of an object. For example, you might try these:

>>> d = Date(11, 8, 2011)
>>> d.isLeapYear()
False

>>> d2 = Date(3, 15, 2012) >>> d2.isLeapYear()
True

>>> Date(1, 1, 1900).isLeapYear() False

# no variable needed!

Just to get a feel for how to test your new datatype, try out the following calls:

# create an object named d with the constructor >>> d = Date(11, 9, 2011)

# show d's value
>>> d
11/09/2011

# a printing example
>>> print ‘Wednesday is’, d Wednesday is 11/09/2011

# create another object named d2 # of *the same date*
>>> d2 = Date(11, 9, 2011)

# show its value
>>> d2
11/09/2011

# are they the same?
>>> d == d2
False

# look at their memory locations
>>> id(d) # return memory address
413488 # your result will be different…

>>> id(d2) # again…
430408 # this should differ from above!

# check if d2 is in a leap year — it’s not! >>> d2.isLeapYear()
False

# yet another object of type Date # next year’s NYDay
>>> d3 = Date(1, 1, 2012)

# check if d3 is in a leap year >>> d3.isLeapYear()
True

def copy(self):
”’Returns a new object with the same month, day, year

as the calling object (self).”’
dnew = Date(self.month, self.day, self.year) return dnew

This method returns a newly constructed object of type Date with the same month, day, and year that the calling object has. Remember that the calling object is named self, so the calling object’s month
is self.month, the calling object’s day is self.day, and so on.

Since you want to create a newly constructed object, you need to call the constructor! This is what you see happening in the copy method.

Try out these examples, which use this year’s New Year’s Day…

>>> d = Date(1, 1, 2011)
>>> d2 = d.copy()
>>> d
01/01/2011

>>> d2
01/01/2011

>>> id(d)
430568
>>> id(d2)
413488
>>> d == d2
False

# your memory address may differ
# but d2 should be different from d! # thus, this should be false…

def equals(self, d2):
”’Decides if self and d2 represent the same calendar date,

whether or not they are the in the same place in memory.”’ return self.year == d2.year and self.month == d2.month and \

           self.day == d2.day

This method should return True if the calling object (named self) and the input (named d2) represent

the same calendar date. If they do not represent the same calendar date, this method should

return False. The examples above show that the same calendar date may be represented at multiple

locations in memory—in that case the == operator returns False. This method can be used to see if two

objects represent the same calendar date, regardless of whether they are at the same location in

memory.

Try these examples (after reloading your file) to get the hang of how this equals method works: >>> d = Date(1, 1, 2011)
>>> d2 = d.copy()
>>> d

01/01/2011

>>> d2
01/01/2011

>>> d == d2

False # this should be False!

>>> d.equals(d2)
True # but this should be True!

>>> d.equals(Date(1, 1, 2011)) # no name needed! True

>>> d == Date(1, 1, 2011) # tests memory addresses False # so it should be False

01/01/2011

>>> d = Date(2, 28, 2012)
>>> d.tomorrow()
>>> d
02/29/2012

>>> d.tomorrow()
>>> d
03/01/2012

>>> d = Date(1, 1, 2011)
>>> d
1/1/2011
>>> d.yesterday()

>>> d
12/31/2010

>>> d = Date(3, 1, 2012)
>>> d.yesterday()
>>> d
02/29/2012

>>> d.yesterday()
>>> d
02/28/2012

>>> d = Date(11, 9, 2011)
>>> d.addNDays(3)
11/09/2011
11/10/2011

11/11/2011
11/12/2011
>>> d
11/12/2011

>>> d = Date(11, 11, 2011) # the near future >>> d.addNDays(1283)
11/11/2011
11/12/2011

… lots of dates skipped … 5/16/2015
5/17/2015
>>> d

5/17/2015 # graduation! (if not before…)

You can check your own additions with this website: http://www.timeanddate.com/date/dateadd.html. Note that 1752 was a weird year for the United States/colonies’ calendar—especially September! However, your Date class does not need to handle these unusual situations (and shouldn’t do so, so that

we can test things consistently!).

>>> d = Date(11, 11, 2011)
>>> d2 = Date(1, 1, 2012)
>>> d.isBefore(d2)
True

>>> d2.isBefore(d)
False
>>> d.isBefore(d)
False

• >>>  d = Date(11,9,2011)
• >>>  d2 = Date(12,16,2011) >>> d2.diff(d)
  37

  >>> d.diff(d2)
  -37
  >>> d
  11/09/2011
  >>> d2 # make sure they did not change… 12/16/2011

  # Here are two that pass over a leap year…

>>> d = Date(11,9,2011) >>> d3 = Date(5, 18, 2012) >>> d3.diff(d)

191

And here are two relatively distant pairs of dates:

>>> d = Date(11, 9, 2011) >>> d.diff(Date(1, 1, 1899)) 41219

>>> d.diff(Date(1, 1, 2101)) -32560

>>> d = Date(12, 7, 1941)
>>> d.dow()
'Sunday'

>>> Date(10, 28, 1929).dow() ‘Monday’

>>> Date(10, 19, 1987).dow() ‘Monday’

>>> d = Date(1, 1, 2100)
>>> d.dow()
'Friday'

# dow is appropriate: crash day! # ditto!

You can check your days of the week at www.timeanddate.com/calendar/ by entering the year you’re interested in.

Congratulations — you now have a Date class whose objects can compute the differences and the days of the week for any calendar dates at all!