Data Structures - Lab 02

Tuesday, September 1st

Objectives:

• Create a Python class

Introduction

Yesterday we started looking at how classes are defined in Python.  We didn't quite make it far enough to justify having you create your own classes completely from scratch.  Instead, you will work with some already written code to describe several classes and then modify this code to add to the class's functionality.

Part A: Creating classes

If you have not already done so, please take the time to read section 8.2 in your textbook.

After you understand the idea behind the code:

• Create a folder called lab2 on your p drive

• Using IDLE enter the code for the die class into a file named die.py.  This is the code from page 304 and the top third of page 305.
• When you feel you have this code completed please compile and test this code by invoking the following commands from the interpreter prompt

    >>> die1 = Die()
    >>> print die1.getValue()
    >>> die1.roll()
    >>> print die1.getValue()
    >>> die1.roll()
    >>> print die1.getValue()
    >>> print die1

• Answer the following questions
  • [Q1]  What is the value printed the first time you invoke getValue()?  Why?
  • [Q2]  What is the value printed the second time you invoke getValue()?  Why?
  • [Q3]  What is the value printed the third time you invoke getValue()?
  • [Q4]  What is the value printed when you entered "print die1"?  Why?

   

• Next, use IDLE to enter the code for the Player class into a file called craps.py.  This code starts a third of the way down page 305 and goes through page 307.  Please notice that the definitions for playOneGame() and playManyGames() are not defined at the class level (under the definition of Player) but at the module level (at the base file level just like the definition for Player itself)
• When you feel you have this code completed please compile and test this code by invoking the following commands from the interpreter prompt:

  >>> playOneGame()
  >>> playOneGame()
  >>> playManyGames()

• Answer the following questions
  • [Q5]  List three examples of the use of Tuples in this code.  For each, how is the tuple actually used?
  • [Q6]  List one example of the use of a list in this code.  How is the list used?
  • [Q7]  Why are the results of the first invocation of playOneGame() not included with the results of the second invocation of playOneGame()?
   

Part B: Reformatting the code

While I understand why your author put the code for playOneGame() and playManyGames() in the same file/module as the code for the player class, I disagree with that design choice.

Separate these two different ideas into two different files by:

• Save a copy of the code from craps.py into a file called player.py. 
• Remove playOneGame() and playManyGames() from player.py so that it only contains the description of the Player class
• Remove the definition of the Player class from craps.py
• In order to allow craps.py to use the Player class (which you just removed) you will need to add a "from X import Y" statement to import Player.  Use the die import statement as a guideline to do this

• When you feel you have this code completed please compile and test this code by loading craps.py and invoking the following commands from the interpreter prompt:

  >>> playOneGame()
  >>> playOneGame()
  >>> playManyGames()

You should get generalized results similar to what you saw in Part B.

[SIG1]  When you get this all working properly demonstrate this code for me and obtain my signature.

Part C: Making a more general Die class

Right now your code will only allow a Die to have six sides.  If you have played a lot of board games you know that dice can come with any number of sides (well, ok, the smallest die you can actually create has four sides).

Modify the code from part A so that

• the constructor for the Die class (__init__) takes in a number of sides as a parameter.
• this number is stored as a variable (similar to _value).
• whenever roll() is invoked it picks a number between 1 and this value rather than 1 and 6

To test this, load the class and create a die with 8 sides:

    >>> die1 = Die(8)

Next, keep running the following lines of code until you get a value of 8 to confirm that you have things set up properly.  While this may take a little while due to random luck it shouldn't take longer than 12-16 rolls

    >>> die1.roll()

    >>> die1.getValue()

Now that you have changed the way that Die works, modify the Player class so that it uses this slightly different form of Die.  This is a simple change, but you will have to think about what changes you just made.

Finally, modify your Player so that he is playing craps with a die of six sides and a die of eight sides, but leave the rest of the game/rules the same. 

Run playManyGames() again to see what effect this has on the players chances of winning versus losing.

[SIG2]  When you get this all working properly demonstrate this code for me and obtain my signature.

Do not forget to “log off” of the machine you are working on before you leave.