Homework 6: Object Oriented Programming
Due by 11:59pm on Friday, 3/15
Instructions
Download hw06.zip. Starter code for the problems can be found in
hw06.py
.
Submission: When you are done, submit with python3 ok
--submit
. You may submit more than once before the deadline; only the
final submission will be scored. Check that you have successfully submitted
your code on okpy.org. See Lab 0 for more instructions on
submitting assignments.
Using Ok: If you have any questions about using Ok, please refer to this guide.
Readings: You might find the following references useful:
Grading: Homework is graded based on effort, not correctness. However, there is no partial credit; you must show substantial effort on every problem to receive any points.
Q0: Survey
Before you get started writing code, please fill out the midterm survey.
Important Submission Note
You're not done yet! Add the passphrase you receive at the end of the survey to passphrase at the top of the homework. For example, if the passphrase was
CS61A
(it isn't 🙂), then the first line of your file should read:
passphrase = 'CS61A'
Instead of:
passphrase = '*** PASSPHRASE HERE ***'
Use Ok to test your code:
python3 ok -q survey
Object Oriented Programming
Q1: Next Fibonacci Object
Implement the next
method of the Fib
class. For this class, the value
attribute is a Fibonacci number. The next
method returns a Fib
instance
whose value
is the next Fibonacci number. The next
method should take only
constant time.
Note that in the doctests, nothing is being printed out. Rather, each call to
.next()
returns a Fib
instance. The way each Fib
instance is displayed is
determined by the return value of its __repr__
method.
Hint: Keep track of the previous number by setting a new instance attribute inside
next
. You can create new instance attributes for objects at any point, even outside the__init__
method.
class Fib():
"""A Fibonacci number.
>>> start = Fib()
>>> start
Fib object, value 0
>>> start.next()
Fib object, value 1
>>> start.next().next()
Fib object, value 1
>>> start.next().next().next()
Fib object, value 2
>>> start.next().next().next().next()
Fib object, value 3
>>> start.next().next().next().next().next()
Fib object, value 5
>>> start.next().next().next().next().next().next()
Fib object, value 8
>>> start.next().next().next().next().next().next() # Ensure start isn't changed
Fib object, value 8
"""
def __init__(self, value=0):
self.value = value
def next(self):
"*** YOUR CODE HERE ***"
def __repr__(self):
return "Fib object, value " + str(self.value)
Use Ok to test your code:
python3 ok -q Fib
Q2: Vending Machine
Create a class called VendingMachine
that represents a vending
machine for some product. A VendingMachine
object returns strings
describing its interactions.
Fill in the VendingMachine
class, adding attributes and methods as
appropriate, such that its behavior matches the following doctests:
class VendingMachine:
"""A vending machine that vends some product for some price.
>>> v = VendingMachine('candy', 10)
>>> v.vend()
'Machine is out of stock.'
>>> v.deposit(15)
'Machine is out of stock. Here is your $15.'
>>> v.restock(2)
'Current candy stock: 2'
>>> v.vend()
'You must deposit $10 more.'
>>> v.deposit(7)
'Current balance: $7'
>>> v.vend()
'You must deposit $3 more.'
>>> v.deposit(5)
'Current balance: $12'
>>> v.vend()
'Here is your candy and $2 change.'
>>> v.deposit(10)
'Current balance: $10'
>>> v.vend()
'Here is your candy.'
>>> v.deposit(15)
'Machine is out of stock. Here is your $15.'
>>> w = VendingMachine('soda', 2)
>>> w.restock(3)
'Current soda stock: 3'
>>> w.restock(3)
'Current soda stock: 6'
>>> w.deposit(2)
'Current balance: $2'
>>> w.vend()
'Here is your soda.'
"""
"*** YOUR CODE HERE ***"
You may find Python string formatting syntax useful. A quick example:
>>> ten, twenty, thirty = 10, 'twenty', [30]
>>> '{0} plus {1} is {2}'.format(ten, twenty, thirty)
'10 plus twenty is [30]'
Use Ok to test your code:
python3 ok -q VendingMachine