mith College Computer Science Week 13 CSC111 Fall 2015 (Lab 12, Homework 12) Dominique Thiébaut

Transcription

1 mith College Computer Science Week 13 CSC111 Fall 2015 (Lab 12, Homework 12) Dominique Thiébaut

2 This Week: Two Concepts Lists of Lists Class Inheritance

3 Lists of Lists (Chapter 11 Designing with Lists and Classes)

4 Two Types of Lists Useful List Operations Two Approaches to Filtering Data Examples

5 Two Types of Lists somelist1 = [ 1, hello, 6.5 ] somelist2 = ( 1, hello, 6.5 )

6 Two Types of Lists somelist1 = [ 1, hello, 6.5 ] somelist2 = ( 1, hello, 6.5 ) mutable immutable

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9 Notation Tuple

10 Two Types of Lists Useful List Operations Two Approaches to Filtering Data Examples

11 Useful List Operations

12 When sorting lists: numbers are sorted in increasing, numerical order strings are sorted in alphabetical order lists of objects cannot be sorted without adding special methods to the classes the objects are derived from ( eq (), lt (), gt (), le (), ge (), ne () )

13 Useful List Operations Sorting Tuples

14 Two Types of Lists Useful List Operations Two Approaches to Filtering Data Examples

15 Examples of Filtering Problems

16 The Problem at Hand Textual Information, in easily splittable form

17 The Problem at Hand OPTION 1: We are only interested in the red information, and only the smaller or larger items Textual Info.

18 The Problem at Hand [ (,, ), (,, ), (,, ), (,, ) ] Textual Info. [ (,, ), (,, ), (,, ), (,, ) ]

19 The Problem at Hand [ (,, ), (,, ), (,, ), (,, ) ] SORT Textual Info. [ (,, ), (,, ), (,, ), (,, ) ]

20 The Problem at Hand OPTION 2: We are only interested in the lines that contain the red information Textual Information, in easily splittable form

21 The Problem at Hand [ (,, ), (,, ), (,, ), (,, ) ] FILTER [ (,, ), (,, ) ] Textual Info.

22 Two Types of Lists Useful List Operations Two Approaches to Filtering Data Examples

23 Example 1

24 10 Rainiest Months In Cambridge, U.K.?

25 # rainycambridge.py # D. Thiebaut # Getting started import urllib.request #--- some constants used by the program --- BASEURL = " def gettemperaturedata( filename ): url = BASEURL + filename print( "Retrieving data from", url ) f = urllib.request.urlopen( url ) data = f.read().decode("utf-8") return data def main(): data = gettemperaturedata( "cambridgedata.txt" ) print( data ) main()

26 We stopped here last time

27 Example 2

28 List of addresses for students enrolled in several classes. Need a list of all Smith students without duplicates and a list of all 5-College students without duplicates

29 Example 3

30 U.S. Presidents 1,George Washington, 2,John Adams, 3,Thomas Jefferson, 42,Bill Clinton, 43,George W. Bush, Filter out Fields 2, 6, and 7 1, George Washington, 30/04/1789, 4/03/1797, Independent, Virginia 2, John Adams, 4/03/1797, 4/03/1801, Federalist, Massachusetts 3, Thomas Jefferson, 4/03/1801, 4/03/1809, Democratic-Republican, Virginia 42, Bill Clinton, 20/01/1993, 20/01/2001, Democratic, Arkansas 43, George W. Bush, 20/01/2001, 20/01/2009, Republican, Texas"""

31 List Operations List Operations Method <list>.append(x) <list>.sort() <list>.reverse() Meaning Add element x to end of list. Sort (order) the list. A comparison function may be passed as a parameter. Reverse the list. <list>.index(x) Returns index of first occurrence of x. <list>.insert(i, x) Insert x into list at index i. <list>.count(x) <list>.remove(x) <list>.pop(i) Returns the number of occurrences of x in list. Deletes the first occurrence of x in list. Deletes the ith element of the list and returns its value. Taken from Zelle's slides:

32 Always start with Small Data Sets

33 Class Inheritance

34 Class Inheritance

35 The Idea

36 Car class - constructor - draw - move - undraw - etc

37 Car class - constructor - draw - move - undraw - etc Wanted with same features but different color

38 Car class - constructor - draw - move - undraw - changecolor - etc Wanted with same features but different color Add new method

39 Car class - constructor - draw - move - undraw - changecolor - etc Wanted: new shape with same features

40 We could write a completely new class for the new car shape But instead, we can save code, save time, save debugging aggravation, by reusing the original car class.

41 We could write a completely new class for the new car shape But instead, we can save code, save time, save debugging aggravation, by reusing the original Car class. We will derive a new class from the Car class. The new class will be derived from it, and will inherit all the member variables and methods. The Car class will become the super class.

42 Another Way to Look at Inheritance valu Class

43 Another Way to Look at Inheritance valu value2 Super Class Derived Class

44 Coding Example

45 The Super Class

46 The Derived Class

47 Creating a Truck Derived from a Car

48 Two Different Syntaxes def draw( self, win ): super().draw( win ) self.top.draw( win ) def draw( self, win ): Car.draw( self, win ) self.top.draw( win )

49 Two Different Syntaxes def draw( self, win ): super().draw( win ) self.top.draw( win ) def draw( self, win ): Car.draw( self, win ) self.top.draw( win ) preferred good when class inherits from two or more super classes

50 Graphics Libraries Are Built on Inheritance: Hierarchy of Classes

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54 A Look at graphics.py

55 Coding Exercise Create a new graphic class called MyCircle, that inherits from Circle, and that contains a circle and a label (text) inside the circle. MyCircle should support the following methods: init ( center, radius, text ) draw( win ) move( dx, dy ) settext( newtext )

56 We stopped here last time

57 Coding Exercise Create an Animal class (name, dob, vaccinated, tattooed) Create a sub-class of Animal: Cow (milkproduction) Create Dog a sub-class of Animal (trained, hospital, seeingdog, rescue) (prog = inheritance5.py)

58 Polymorphism

59 Polymorphism

60 Poly = Many Morph = Form, Shape

61 Poly = Many Morph = Form, Shape Image taken from

62 Poly = Many Morph = Form, Shape Speak() Image taken from

63 Poly = Many Morph = Form, Shape Speak() Image taken from

64 Poly = Many Morph = Form, Shape Speak() Image taken from

65 Poly = Many Morph = Form, Shape Polymorphism is the ability for a function, or method, to behave differently depending on which class it belongs to, or what type of parameter is given to it. Image taken from

66 Let's Code this!

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70 Polymorphism Polymorphism Polymorphism

71 Overloading

72 Another Example of Polymorphism: the + operator

73 Another Example of Polymorphism: the + operator

74 Another Example of Polymorphism: the + operator Overloading

75 Abundant syntax brings more burden than help. Guido van Rossum

76 Abundant and del from not while syntax brings as elif global or with assert else if pass yield break except import print more burden class exec in raise continue finally is return than help. def for lambda try Guido van Rossum