mith College Computer Science Week 9 CSC111 - Fall 2018 Dominique Thiébaut

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1 mith College Computer Science Week 9 CSC111 - Fall 2018 Dominique Thiébaut dthiebaut@smith.edu

2 Dealing with Exceptions (Chapter 7.4) Defining Classes (Chapter 10)

3 # getinput: returns an integer larger # than 0. Expected to be robust def getinput(): while True: x = eval( input( "Enter a positive int: " ) ) if x >= 0: return x print( "Invalid number: Please try again: " ) def main(): num = getinput() print( "you entered", num ) main()

5 Exception

6 RAM Processor Keyboard Disk Python Program Network

7 RAM Processor Keyboard Operating System Disk Python Program Network

8 RAM Processor Keyboard Operating System Disk Python Program Events Network

9 RAM Processor Keyboard Operating System Disk Python Program Exception Network

10 Exception Some exceptions are generated by the Python interpreter

11 RAM Processor Keyboard Operating System Disk Python Program Exception Network

12 RAM Processor Keyboard Operating System Disk Python Program Network

13 RAM Processor Keyboard Operating System Disk Python Program Network If Exception generated by Python Interpreter, OS "kills" the Python Program

14 RAM Processor Keyboard Operating System Disk Python Program We want to prevent exceptions from going all the way up to the operating system Network

15 Python Program

16 Python Program We want to "isolate" dangerous code areas We want a tight isolation blocks around the potentially dangerous code sections

17 Coding exceptions is a pain in the neck but exceptions are an integral part of programming

18 Try/Except Statement try: python code that might generate an exception Except exceptionxyz : python code to run in case there's an exception

21 Solution

22 Approach to Handling Exceptions 1. Run code without try/except statements 2. Test thoroughly 3. Fix whatever can be fixed with "regular" python code 4. Record all exceptions that cannot be fixed otherwise, and add try/except to catch them. 5. Make the try section as small as possible.

23 Multiple Exceptions (taken from Zelle)

24 Solving Equation of Degree 2

25 Solving Equation of Degree 2

26 Hardening the Function

27 Dealing with Exceptions (Chapter 7.4) CSV Files Defining Classes (Chapter 10)

28 CSV Format Comma-Separated Values Very popular way of representing information where all records have the same format Easy to implement Examples: data/csv/csv.html

29 Example "Name", "Sex", "Age", "Height (in)", "Weight (lbs)" "Alex", "M", 41, 74, 170 "Bert", "M", 42, 68, 166 "Carl", "M", 32, 70, 155 "Dave", "M", 39, 72, 167 "Elly", "F", 30, 66, 124 "Fran", "F", 33, 66, 115 "Gwen", "F", 26, 64, 121 "Hank", "M", 30, 71, 158 "Ivan", "M", 53, 72, 175 "Jake", "M", 32, 69, 143 "Kate", "F", 47, 69, 139 "Luke", "M", 34, 72, 163 "Myra", "F", 23, 62, 98 "Neil", "M", 36, 75, 160 "Omar", "M", 38, 70, 145 "Page", "F", 31, 67, 135 "Quin", "M", 29, 71, 176 "Ruth", "F", 28, 65, 131

30 Reading CSV Files

31 CSV and MS Excel

32 CSV and MS Excel

33 Dealing with Exceptions (Chapter 7.4) CSV Files Defining Classes (Chapter 10)

34 Dealing with Exceptions (Chapter 7.4) CSV Files Defining Classes (Chapter 10)

35 Coding Dice

36 Using the Objects # Create 2 dice, one with 6 sides, one with 8 d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() )

37 We need to create the blueprint for a box (object) value nosides roll()

38 We need to create the blueprint for the box value nosides getvalue()

39 Blueprint class def

40 Blueprint class def blueprint object

41 object Blueprint class def blueprint object

42 object object Blueprint class def blueprint object

43 object object Blueprint class def blueprint = class object

44 A Class for a Die # libraries from random import randrange # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 Blueprint class def def roll( self ): self.value = randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

45 A Die Class # libraries import random constructor # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

46 A Die Class # libraries import random # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

47 A Die Class # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) Die. init (6) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) # libraries import random # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

48 A Die Class # libraries import random # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 reference to the object def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

49 A Die Class # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) # libraries import random # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value must be 1st param of all methods

50 A Die Class # libraries import random # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) roll(d1) roll(d2) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

51 A Die Class # libraries import random # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 makes the variable a "member" of the object def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

52 Playing dice

53 We stopped here last time

54 Homework Programs Great Organization!

55 Homework Programs No main() function. Not Documented

56 Homework Programs Nice Job!

57 From Now On

58 All Programs Submitted

59 Must Be Documented

60 Or Else!

61 Up to 1 Letter Grade Down, For the whole assignment if Documentation Missing

Min/Max Revisited who is associated with the largest number? Alex, 3 Max, 4 Sophia, 10 Lujun, 2 Maggie, 5 Photo credit: https://www.dreamstime.

62 Min/Max Revisited who is associated with the largest number? Alex, 3 Max, 4 Sophia, 10 Lujun, 2 Maggie, 5 Photo credit:

63 Classes and Objects

64 A Die Class from dieclass import Die def main(): # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) main() # dieclass.py # Definition for a die class. import random # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value playdice.py dieclass.py

65 Why Create a Die Class? Randint Could have Sufficed Modularity Details are hidden (Information hiding) The Die class can easily be enhanced/modified without having to change main program die with a bias history of rolls keeping track of statistics

66 Write a program that maintains a list of cat objects. Cats have a name, a breed, may or may not be vaccinated, and have an age expressed in years. Exercise Image credits: nicepixy.net

67 Examples Minou, 3, vac, stray Max, 1, not-vac, Burmese Gizmo, 2, vac, Bengal Garfield, 4, not-vac, Orange Tabby

68 Using Cat Objects # Example: using a cat object # Minou, 3, vac, stray cat1 = Cat( Minou, True, stray, 3 ) # Print if cat is vaccinated or not if cat1.isvaccinated(): print( cat1.getname(), is vaccinated ) else: print( cat1.getname(), is not vaccinated )

69 Wanted: A program that - outputs all the cats - outputs only the vaccinated cats - outputs the cats 2 or older

70 Good Methods To Start With When Creating a Class Constructor init () Inspector Methods getvalue() Mutator Methods roll() Default string representation str ()

71 We stopped here last time

72 Converting A String to a Boolean

73 Converting A String to a Boolean

74 Converting A String to a Boolean

75 Converting A String to a Boolean

76 Converting A String to a Boolean

77 Important Concepts: LOCAL vs. GLOBAL

78 What can you say about this program? Focus on the variable a

79 Local Variable What can you say about this program? Focus on the variable a

80 Local Variable Error! What can you say about this program? Focus on the variable a

81 Local Variable Error! Local Variable What can you say about this program? Focus on the variable a

82 What can you say about this new program? Focus on the variable a

83 30 30

84 Global Variable 30 30

85 What can you say about this third program? Focus on the variable a

87 Global Variable Local Variable

88 What can you say about this fourth program? Focus on the variable a

90 Review

91 Review Blueprint class def

92 Review Blueprint class def

93 Review Blueprint class def

94 Review Blueprint class def value

95 Review Blueprint class def value

96 Review Instantiation: Object is instance of a Class Blueprint class def member variable instance variable value Class method

97 Review: A Die Class # libraries import random # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

98 Review: A Die Class WHY self.? # Create 2 dice, one with 6 sides d1 = Die( 6 ) d2 = Die( 8 ) # Roll both dice d1.roll( ) d2.roll( ) # display their value print( "Die 1: ", d1.getvalue() ) print( "Die 2: ", d2.getvalue() ) # libraries import random # a class for a die class Die: def init ( self, n ): self.nosides = n self.value = 1 def roll( self ): self.value = random.randrange( 1, self.nosides+1 ) def getvalue( self ): return self.value

99 Pair Programming in Lab 9 Review of Classes and Objects Cats, Cats, Cats Default string representation List of Cats Reading CSV Files of Cats Searching for a Cat in a List

100 Back to Cats

101 Using Cat Objects # Minou, 3, vaccinated, stray cat1 = Cat( Minou, True, stray, 3 ) if cat1.isvaccinated(): print( cat1.getname(), is vaccinated ) else: print( cat1.getname(), is not vaccinated )

102 Step 1: Implement the Class

103 Step 2: Create a List of Cats

104 Step 3: Read a CSV File of Cats

105 Step 4: Display Only Vaccinated Cats

106 Step 5: Search for the Youngest Cat

107 Looping through a list of objects Object-Oriented Graphics

108 Graphic Cars Moving Around

109 Car Geometry

110 e Demo T mo Time Demo Ti Time Demo Time Demo e Demo Time Demo Time emo Time Demo Time Demo Time Demo Time Demo Time Demo Time Demo Time D e Demo Time Demo Time Demo T Time D Demo Time!

111 Inspiration

112 Video 1

113 Video 2

114 Video 3

mith College Computer Science Lecture Notes CSC111 Week 7 Spring 2018 Dominique Thiébaut

mith College Computer Science Lecture Notes Week 7 Spring 2018 CSC111 Dominique Thiébaut dthiebaut@smith.edu Midterm Grades available later today (3/19/18) Outline A Second Look at Files Reading Files