In-class notes for 04/09/2014

CS 121B (CS1), Spring 2014

• Homework assignment

• Quiz

Submitted questions on assignments and technology

• Seeing Python3 return values.

  • Four ways to run Python3: book ActiveCode windows (can use print() to see return values); idle3 on a Link machine (interactive, i.e., return values are shown for each instruction before you enter the next instruction); using python3 interactively on a link machine (also shows return values); using python3 with your program as a command-line argument (can use print() to see return values)

• ______

Upcoming

• Homework 23

• Science Symposium

  • Four events, all in Tomson 280

    • Thursday 7pm panel -- 4 points EC for a half-page response

    • Friday 3:00pm speaker -- 2 point EC for a half-page response

    • Friday 4:30pm speaker -- 2 point EC for a half-page response

    • Friday 7:30pm CS speaker -- 4 points EC for a half-page response

Submitted questions on readings

Defining classes

• review of OO terminology: object, method, state variable, class.

• Example of spec and definition of a class (Account)

  1. State variables are implicitly declared. (We will list them in comments.)

         class Account:
             # state variables:
             #   balance -- float, represents the account balance
             #   initBal -- float, represents the initial account balance
     

  2. Methods include an extra initial argument usually called self, representing the object whose method is being called.

         class Account:
             ...
         
             def getBalance(self):
                 return self.balance
         
             def getInitBal(self):
                 return self.initBal
         
             def deposit(self, amt):
                 self.balance = self.balance + amt
                 return self.balance
         
             def withdraw(self, amt):
                 self.balance = self.balance - amt
                 return self.balance
     
     

     These methods are called as follows:

         a1 = Account(...)  # fill in argument for constructor
         a1.deposit(100.50)
         print( a1.getBalance() )
     

  3. A class's constructor is a function for initializing new objects.

     In Python, a class's constructor is called __init__, and the constructor is defined like a method.

         class Account:
     	...
     
             def __init__(self, bal):
                 self.balance = bal
                 self.initBal = bal
     

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