1. EECS 110: Lec 11: Indefinite Loops and Program Design
Aleksandar Kuzmanovic
Northwestern University

2. Final Exam When: Where: Time: Wednesday 5/31/17
Pancoe Life Science Pavilion (PLSAUD)
Time:
9:30AM – 11:30AM

3. Python and images for creating and saving images import bmp.py
image = BitMap( 300, 200, Color.GREEN )
creates a bitmap object
and names it image

4. Python and images import bmp.py for creating and saving images
image = BitMap( 300, 200, Color.GREEN )
creates a bitmap object
and names it image
objects are software abstractions containing structured information

5. Python and images and objects
import bmp.py
image = BitMap( 300, 200, Color.GREEN )
here, a bitmap object named image
is calling an internal method named saveFile
image.saveFile( "test.bmp" )
objects are variables that can contain their own functions, often called methods

6. Python and images and objects
import bmp.py
image = BitMap( 300, 200, Color.GREEN )
image.setPenColor( Color.Red )
two more internal methods
image.plotPixel( 150, 100 )
image.saveFile( "test.bmp" )
objects are variables that can contain their own functions, often called methods

7. Q: What does this plot? from bmp import * def test():
""" image demonstration """
width = 200
height = 200
image = BitMap( width, height )
# a 2d loop over each pixel
for col in range(width):
for row in range(height):
if col == row:
image.plotPoint( col, row )
image.saveFile( "test.bmp" )

8. A: A diagonal in the SW -> NE direction
Q: What does this plot?
A: A diagonal in the SW -> NE direction
from bmp import *
def test():
""" image demonstration """
width = 200
height = 200
image = BitMap( width, height )
# a 2d loop over each pixel
for col in range(width):
for row in range(height):
if col == row:
image.plotPoint( col, row )
image.saveFile( "test.bmp" )

9. How could you change this code so that it plots a diagonal from NW to SE?
def test():
""" demonstrating images """
width = 200
height = 200
image = BitMap( width, height )
# a 2d loop over each pixel
for col in range(width):
for row in range(height):
if col == row:
image.plotPoint( col, row )
image.saveFile( "test.bmp" )

10. How could you change this code so that it plots a diagonal from NW to SE?
def test():
""" demonstrating images """
width = 200
height = 200
image = BitMap( width, height )
# a 2d loop over each pixel
for col in range(width):
for row in range(height):
if col == height – row -1:
image.plotPoint( col, row )
image.saveFile( "test.bmp" )

11. Input and typing trouble!
print('Please input a number of meters’)
meters = input() # get input from user
cm = meters * # convert to centimeters
print('That is', cm, 'cm.’) # print out the result

12. Input and typing trouble!
print('Please input a number of meters')
meters = input() # get input from user
cm = meters * # convert to centimeters
print('That is', cm, 'cm.’) # print out the result
>>>
Please input a number of meters 5
That is cm.
What is python thinking ?!?

13. Fix #1: use a type converter
print('Please input a number of meters’)
meters = int(input())
cm = meters * 100
print('That is', cm, 'cm.')
check out my newly installed int converter! 1
100
The type of variable (box) matters!
name: meters type: int
name: cm
type: int

14. Fix #1: use a type converter
print('Please input a number of meters')
meters = int(input()) # get int input from user
cm = meters * 100
print('That is', cm, 'cm.')
print('Please input a number of meters')
meters = float(input()) # get float input from user
cm = meters * 100
print('That is', cm, 'cm.')
str converts to string type

15. s ='gattacaaggtaaaatgca'
More with Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

16. s ='gattacaaggtaaaatgca'
Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

17. s ='gattacaaggtaaaatgca'
Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
s = 'gattacaaggtaaaatgca'
N = 0
for i in range(0,len(s)):
if s[i] == 'a':
N = N + 1
print('N is', N)
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

18. s = 'gattacaaggtaaaatgca'
Loopy thinking
s = 'gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

19. s = 'gattacaaggtaaaatgca'
Loopy thinking
s = 'gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
s = 'gattacaaggtaaaatgca'
N = 0
for i in range(0,len(s)):
if s[i] == 'a' or s[i] == 't':
N = N + 1
print('N is', N)
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

20. s ='gattacaaggtaaaatgca'
Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

21. s ='gattacaaggtaaaatgca'
Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
s = 'gattacaaggtaaaatgca'
N = 0
for i in range(1,len(s)):
if s[i] == 'a' and s[i-1] == 't':
N = N + 1
print('N is', N)
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

22. s ='gattacaaggtaaaatgca'
Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
s = 'gattacaaggtaaaatgca'
N = 0
for i in range(1,len(s)):
if s[i] == 'a' and s[i-1] == 't':
N = N + 1
print('N is', N)
How could we find the number of 'a's ? How about 'a's or 't's?
How could we find the number of 'ta's ?
How could we find the longest sequence of 'a's ?

23. s ='gattacaaggtaaaatgca'
Loopy thinking
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
How could we find the longest sequence of 'a's ?

24. s ='gattacaaggtaaaatgca‘
Loopy thinking
s ='gattacaaggtaaaatgca‘
- Len of current run
- Len of best run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
How could we find the longest sequence of 'a's ?

25. s ='gattacaaggtaaaatgca'
Planning in "pseudocode"
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Keep track of CurRun, MaxRun
Loop through the string:
if we do see an 'a'
if the PREVIOUS letter is NOT an 'a'
if the PREVIOUS letter IS an 'a'

26. s ='gattacaaggtaaaatgca'
Planning in "pseudocode"
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Keep track of CurRun, MaxRun
Loop through the string:
if we do see an 'a'
if the PREVIOUS letter is NOT an 'a'
Start a Run! CurRun = 1
if the PREVIOUS letter IS an 'a'
Continue our run! CurRun = CurRun + 1
Check for a new maximum…

27. s ='gattacaaggtaaaatgca'
Planning in "pseudocode"
s ='gattacaaggtaaaatgca' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
MAX = 0
cur = 0
for i in range(0,len(s)):
if s[i] == 'a':
if s[i-1] != 'a':
cur = 1
else:
cur = cur + 1
if cur > MAX:
MAX = cur
print('Max is', MAX)
Keep track of CurRun, MaxRun
Loop through the string:
if we do see an 'a'
if the PREVIOUS letter is NOT an 'a'
Start a Run!
if the PREVIOUS letter IS an 'a'
Continue our run!
Check for a new maximum…

28. Summary 1 2 4 3 s = 'gattacaaggtaaaatgca' N = 0
for i in range(0,len(s)):
if s[i] == 'a':
N = N + 1
print('N is', N) 2
s = 'gattacaaggtaaaatgca'
N = 0
for i in range(0,len(s)):
if s[i] == 'a' or s[i] == 't':
N = N + 1
print('N is', N) 4
s = 'gattacaaggtaaaatgca'
MAX = 0
cur = 0
for i in range(0,len(s)):
if s[i] == 'a':
if s[i-1] != 'a':
cur = 1
else:
cur = cur + 1
if cur > MAX:
MAX = cur
print 'Max is', MAX) 3
s = 'gattacaaggtaaaatgca'
N = 0
for i in range(1,len(s)):
if s[i] == 'a' and s[i-1] == 't':
N = N + 1
print('N is', N)

29. for while Loops definite iteration indefinite iteration
For a known number of iterations
For an unknown number of iterations

30. Seeing into the future…
def menu():
choice = 1 # Anything except 9
while choice != 9:
print("I see danger in your future...")
printMenu()
choice = input("Make your choice ")
print("The inner eye can see no more")
def printMenu():
print("What would you like to do?")
print("\t 0: See another prediction")
print("\t 9: Quit")
"\t " represents a tab

31. Gimme a break break stops the execution of the current loop
I'll figure out later how to get out of this loop!
def menu():
while True:
print("I see danger in your future...”)
printMenu()
choice = int(input("Make your choice "))
if choice == 9:
break
print("The inner eye can see no more")
def printMenu():
print("What would you like to do?")
print("\t 0: See another prediction")
print("\t 9: Quit")
OK – I'll stop the loop now and continue with the code after the loop
break stops the execution of the current loop

32. Indefinite Loops + input
A problem this week ask you to repeatedly interact with the user
(TTSecurities)
What would you like to do?
0: Enter a new list
1: Print the current list
2: Find the average
9: Quit
Please enter your choice
The user's choice controls what happens

33. Indefinite Loops + input
def menu():
choice = 1
while choice != 9:
printMenu()
choice = int(input("Please enter your choice "))
if choice == 0:
print("You chose to enter a new list”)
elif choice == 1:
print("You chose to print the list")
elif choice == 2:
print("You chose to find this average of the list")
elif choice != 9:
print("You made an invalid choice")
print("Goodbye!")
def printMenu():
print("What would you like to do?")
print("\t 0: Enter a new list")
print("\t 1: Print the current list")
print("\t 2: Find the average")
print("\t 9: Quit")

34. if vs elif What happens if we change the elifs to ifs? def menu():
choice = 1
while choice != 9:
printMenu()
choice = int(input("Please enter your choice "))
if choice == 0:
print("You chose to enter a new list")
if choice == 1:
print("You chose to print the list")
if choice == 2:
print("You chose to find this average of the list")
if choice != 9:
print("You made an invalid choice")
print("Goodbye!”)
What happens if we change the elifs to ifs?

35. Indefinite Loops + input
def menu():
choice = 1
L = []
while choice != 9:
printMenu()
choice = int(input("Please enter your choice "))
if choice == 0:
L = getNewList()
elif choice == 1:
printList(L)
elif choice == 2:
averageList(L)
elif choice != 9:
print("You made an invalid choice")
print("Goodbye!")
def getNewList():
print("You chose to get a new list")
return []
Making a function for each choice makes the code cleaner and easier to modify

36. Gimme another break def menu(): choice = 1 L = [] while True:
printMenu()
choice = int(input("Please enter your choice "))
if choice == 0:
L = getNewList()
elif choice == 1:
printList(L)
elif choice == 2:
averageList(L)
elif choice == 9:
break
else:
print("You made an invalid choice")
print("Goodbye!”)

37. The Price Is Right!
Goal: Buy from a set of 5 items (as many of each as you want) while spending between $9.25
and $10.00.

38. Step 1: Identify Information To Store
What information does this program need to keep track of?
Money you have spent, how much each item is,
Items, # items to buy, limits,

39. Step 1: Identify Information To Store
How much has the user spent?
float: money
Which items are available?
list of strings: items
How much does each available item cost?
list of floats: prices
Which item did the user currently choose?
int: choice
How many of the currently chosen item does the user want?
int: number
Money you have spent, how much each item is,
Items, # items to buy, limits,

40. Step 1: Identify Information To Store
How much has the user spent?
float: money
Which items are available? [“coke”, “ramer”]
list of strings: items
How much does each available item cost?
list of floats: prices
Which item did the user currently choose?
int: choice
How many of the currently chosen item does the user want?
int: number
Money you have spent, how much each item is,
Items, # items to buy, limits,

41. Step 1: Identify Information To Store
How much has the user spent?
float: money
Which items are available? [“coke”, “ramer”]
list of strings: items
How much does each available item cost?
list of floats: prices [ 0.75, 0.25]
Which item did the user currently choose?
int: choice
How many of the currently chosen item does the user want?
int: number
Money you have spent, how much each item is,
Items, # items to buy, limits,

42. Step 2: Break Down Functionality
What are the things that this program needs to do?
Allow user to buy one item
Ask user how many items to buy
Update $$, update item list, check if finished

43. Step 2: Break Down Functionality
Control the overall game play
Prompt the user to enter a choice and number of items
Calculate the total spent
Figure out when the game is over
Figure out win or lose
Print a welcome message
Remove the purchased item from the lists (items, prices)
Allow user to buy one item
Ask user how many items to buy
Update $$, update item list, check if finished

44. ID problems, write on board
Attempt 1
def playTry1():
print("Welcome to the price is right!")
print("Your goal is to buy 5 or fewer items (any number of each)")
print("and spend between $9.25 and $10")
items = ["bleach","coke","ramen","ice cream","super ball"]
prices = [1.35, .75, .25, 3.00, 1.75]
money = 0.0
while money < 9.25 and len(items) > 0:
print("You have spent $", money)
printItems( items )
choice = int(input( "Which item would you like to buy? "))
number = int(input( "How many "+items[choice]+" would you like?"))
print(items[choice], "is $", prices[choice])
money += prices[choice]*number
prices = prices[0:choice] + prices[choice+1:]
items = items[0:choice] + items[choice+1:]
if money >= 9.25 and money <= 10.0:
print("You win!")
else:
print("You lose!”)
ID problems, write on board

45. "Quiz" part 1: Print Items Allow user to buy one item
>>> items = [“coke”, “pepsi”, “sprite”]
>>> printItems(items)
0 : coke
1 : pepsi
2 : sprite
Allow user to buy one item
Ask user how many items to buy
Update $$, update item list, check if finished

46. ID problems, write on board
Attempt 1
def playTry1():
print("Welcome to the price is right!")
print("Your goal is to buy 5 or fewer items (any number of each)")
print("and spend between $9.25 and $10")
items = ["bleach","coke","ramen","ice cream","super ball"]
prices = [1.35, .75, .25, 3.00, 1.75]
money = 0.0
while money < 9.25 and len(items) > 0:
print("You have spent $", money)
printItems( items )
choice = int(input( "Which item would you like to buy? "))
number = int(input( "How many "+items[choice]+" would you like?"))
print(items[choice], "is $", prices[choice])
money += prices[choice]*number
prices = prices[0:choice] + prices[choice+1:]
items = items[0:choice] + items[choice+1:]
if money >= 9.25 and money <= 10.0:
print("You win!")
else:
print("You lose!”)
ID problems, write on board

47. ID problems, write on board
Attempt 1: Issues
def playTry1():
print("Welcome to the price is right!")
print("Your goal is to buy 5 or fewer items (any number of each)")
print("and spend between $9.25 and $10")
items = ["bleach","coke","ramen","ice cream","super ball"]
prices = [1.35, .75, .25, 3.00, 1.75]
money = 0.0
while money < 9.25 and len(items) > 0:
print("You have spent $", money)
printItems( items )
choice = int(input("Which item would you like to buy? "))
number = int(input("How many "+items[choice]+" would you like?"))
print(items[choice], "is $", prices[choice])
money += prices[choice]*number
prices = prices[0:choice] + prices[choice+1:]
items = items[0:choice] + items[choice+1:]
if money >= 9.25 and money <= 10.0:
print("You win!")
else:
print("You lose!”)
ID problems, write on board
Magic numbers!

48. ID problems, write on board
Attempt 1a
def playTry1a():
LIMIT_MIN = LIMIT_MAX = 10.00
items = ["bleach","coke","ramen","ice cream","super ball"]
prices = [1.35, .75, .25, 3.00, 1.75]
money = 0.0
print("Welcome to the price is right!")
print("Your goal is to buy", len(items), "or fewer items…")
print("and spend between $", LIMIT_MIN, "and $", LIMIT_MAX)
while money < LIMIT_MIN and len(items) > 0:
print("You have spent $", money
printItems( items )
choice = int(input("Which item would you like to buy? "))
number = int(input("How many "+items[choice]+" would you like?"))
print(items[choice], "is $", prices[choice] )
money += prices[choice]*number
prices = prices[0:choice] + prices[choice+1:]
items = items[0:choice] + items[choice+1:]
print("You have spent $", money)
if money >= LIMIT_MIN and money <= LIMIT_MAX:
print("You win!")
else:
print("You lose!”)
ID problems, write on board

49. ID problems, write on board
Attempt 1a: Issue
def playTry1a():
LIMIT_MIN = LIMIT_MAX = 10.00
items = ["bleach","coke","ramen","ice cream","super ball"]
prices = [1.35, .75, .25, 3.00, 1.75]
money = 0.0
print("Welcome to the price is right!")
print("Your goal is to buy", len(items), "or fewer items…")
print("and spend between $", LIMIT_MIN, "and $", LIMIT_MAX)
while money < LIMIT_MIN and len(items) > 0:
print("You have spent $", money)
printItems( items )
choice = int(input("Which item would you like to buy? ”))
number = int(input("How many "+items[choice]+" would you like?”))
print(items[choice], "is $", prices[choice] )
money += prices[choice]*number
prices = prices[0:choice] + prices[choice+1:]
items = items[0:choice] + items[choice+1:]
if money >= LIMIT_MIN and money <= LIMIT_MAX:
print("You win!")
else:
print("You lose!”)
ID problems, write on board
Functionality is not broken out

50. Code is self-commenting.
Each function does one specific thing. It's clear where we go to change aspects of the game.
Code is self-commenting.
def playBetter():
""" Play the game """
[items, prices] = initilizeItems()
LIMIT_HIGH = 10.00
LIMIT_LOW = 9.25
money = 0.0
printIntro(LIMIT_LOW, LIMIT_HIGH, items)
while not allDone(items, LIMIT_LOW, money):
print("You have spent $", money)
[items, prices, spent] = playRound(items, prices)
money += spent
winOrLose(money, LIMIT_LOW, LIMIT_HIGH)
Functions can return
more than one thing in a list

51. def playRound(items, prices):
""" Play one round of the game
Inputs: A list of items and a list of prices
Returns: [items, prices, spent] where items is list of items remaining,
prices is a list of remaining prices,
and spent is the amount spent this round"""
print("*********************”)
printItems( items )
choice = int(input("Which item would you like to buy? "))
number = int(input("How many " + items[choice] +" would you like? "))
print(items[choice], "is $", prices[choice])
spent = prices[choice]*number
prices = prices[0:choice] + prices[choice+1:]
items = items[0:choice] + items[choice+1:]
return [items, prices, spent]

52. (That is, you don’t have to get it perfect the first time)
You CAN (and should) modify your code as you go to make it cleaner and better organized.
(That is, you don’t have to get it perfect the first time)
def playBetter():
""" Play the game """
[items, prices] = initilizeItems()
LIMIT_HIGH = 10.00
LIMIT_LOW = 9.50
money = 0.0
printIntro(LIMIT_LOW, LIMIT_HIGH, items)
while not allDone(items, LIMIT_LOW, money):
print("You have spent $", money)
[items, prices, spent] = playRound(items, prices)
money += spent
winOrLose(money, LIMIT_LOW, LIMIT_HIGH)

53. "Quiz" def diff( L ): def printItems( items ):
Name(s):_______________________________
Return the min difference between any 2 elements in L
Example:
Print a list of strings with the specified format
>>> diff([7, 0, 6, 4]) 1
Example:
>>> items = [“coke”, “pepsi”, “sprite”]
>>> printItems(items)
0 : coke
1 : pepsi
2 : sprite
Only consider unsigned differences.
You can assume at least 2 elements in the list
Hint: use a NESTED loop
def diff( L ):
You need determine each element's index…
def printItems( items ):

54. "Quiz" part 1: Print Items Allow user to buy one item
>>> items = [“coke”, “pepsi”, “sprite”]
>>> printItems(items)
0 : coke
1 : pepsi
2 : sprite
Allow user to buy one item
Ask user how many items to buy
Update $$, update item list, check if finished

55. "Quiz" part 1: Print Items Allow user to buy one item
>>> items = [“coke”, “pepsi”, “sprite”]
>>> printItems(items)
0 : coke
1 : pepsi
2 : sprite
def printItems(items):
for x in range(len(items)):
print(x,”:”,items[x])
Allow user to buy one item
Ask user how many items to buy
Update $$, update item list, check if finished

56. "Quiz" part 1: Print Items Allow user to buy one item
>>> items = [“coke”, “pepsi”, “sprite”]
>>> printItems(items)
0:coke
1:pepsi
2:sprite
def printItems(items):
for x in range(len(items)):
print(str(x)+”:”+items[x])
, in print automatically puts blank space
+ removes blank space
Allow user to buy one item
Ask user how many items to buy
Update $$, update item list, check if finished

57. Return the min difference between any 2 elements in L
"Quiz" Part 2
Return the min difference between any 2 elements in L
Example:
>>> diff([7, 0, 6, 4]) 1
Only consider unsigned differences.
You can assume at least 2 elements in the list
Hint: use a NESTED loop
def diff( L ):

58. Return the min difference between any 2 elements in L
"Quiz" Part 2
Return the min difference between any 2 elements in L
Example:
>>> diff([7, 0, 6, 4]) 1
Only consider unsigned differences.
You can assume at least 2 elements in the list
Hint: use a NESTED loop
def diff( L ):
mindif = abs(L[1] – L[0])
for i in range(len(L)-1):
for j in range(i+1,len(L)):
d = abs(L[i]-L[j])
if d < mindiff:
mindiff = d
return mindif