Description
Task 1: “Reference” Variables and Objects (a) What does the program below print? (Class Point is a simplified version of the class we designed in class). IMPORTANT: notice that the function riddle is outside of Point class (pay attention to what is lined up) (b) http://www.pythontutor.com/visualize.html#mode Open file t1.py and copy it in Python Vizualizer. Make sure you understand what is happening with variables as you step through the execution of the program.
Task 2: “Reference” Variables and Objects (a) What does the program below print? (Class Point is a simplified version of the class we designed in class) (b) http://www.pythontutor.com/visualize.html#mode Open file t2.py and copy it in Python Vizualizer. Make sure you understand what is happening with variables as you step through the execution of the program.
Task 3: “Reference” Variables and Objects (a) What does the program on the left prints? The objects you design are MUTABLE. (b) Open file t3.py and copy it in Python Vizualizer. Make sure you understand what is happening with variables as you step through the execution of the program.
Task 4: “Reference” Variables and Objects (a) What does the program on the left prints? (b) Open file t3.py and copy it in Python Vizualizer. Make sure you understand what is happening with variables as you step through the execution of the program. A class method is really a function defined in the class namespace; when Python executes it first translates it to and actually executes this last statement Introduction to Computing Using Python Class methods (REVIEW) >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> __add__ list __add__() sort() count x count() pop pop() . . . >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> lst.append(6) >>> lst [1, 2, 3, 7, 8, 9, 6] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> lst.append(6) >>> lst [1, 2, 3, 7, 8, 9, 6] >>> list.append(lst, 5) >>> lst [1, 2, 3, 7, 8, 9, 6, 5] lst.sort() list.sort(lst) lst.append(6) instance.method(arg1, arg2, …) list.append(lst, 6) class.method(self, arg1, arg2, …) The function has an extra argument, which is the object invoking the method
Task 5: Methods class translation to Function calls – Open the file called t5.py and translate all the indicated method calls to equivalent function calls – Once done run those function calls in Python shell to observe that they indeed are equivalent to their method call couterparts
Programming exercise 1: Open file lab10.py It contains the classes we developed during lectures last week. Do the following exercises: A) Add method distance to the class Point. It takes another Point object as input and returns the distance to that point (from the point invoking the method). (Recall that you need to import math to get sqrt function) >>> c = Point(0,1) >>> d = Point(1,0) >>> c.distance(d) 1.4142135623730951 B) Add to class Point methods up, down, left, and right that move the Point object by 1 unit in the appropriate direction. The implementation of each should not modify instance variables x and y directly but rather indirectly by calling existing method move(). >>> a = Point(3, 4) >>> a.left() >>> a.get() (2, 4) C) In to class Animal modify the constructor to set age of the Animal object. Also add method getAge to retrieve the age of the Animal object. >>> flipper = Animal(‘dolphin’, ‘?’, 3) >>> flipper.getAge() 3 Operator Method x + y x.__add__(y) x – y x.__sub__(y) x * y x.__mul__(y) x / y x.__truediv__(y) x // y x.__floordiv__(y) x % y x.__mod__(y) x == y x.__eq__(y) x != y x.__ne__(y) x > y x.__gt__(y) x >= y x.__ge__(y) x < y x.__lt__(y) x <= y x.__le__(y) repr(x) x.__repr__() str(x) x.__str__() len(x) x.__len__() (x) .__init__(x) Introduction to Computing Using Python Python operators In Python, all expressions involving operators are translated into method calls >>> ‘!’*10 ‘!!!!!!!!!!’ >>> [1,2,3] == [2,3,4] False >>> 2 < 5 True >>> ‘a’ <= ‘a’ True >>> len([1,1,2,3,5,8]) 6 >>> repr([1,2,3]) ‘[1, 2, 3]’ >>> repr(193) ‘193’ >>> repr(set()) ‘set()’ Built-in function repr()returns the canonical string representation of an object >>> [1,2,3] [1, 2, 3] >>> 193 193 >>> set() set() >>> [1,2,3].__repr__() ‘[1, 2, 3]’ >>> int(193).__repr__() ‘193’ >>> set().__repr__() ‘set()’ • This is the representation printed by the shell when evaluating the object >> ‘!’.__mul__(10) ‘!!!!!!!!!!’ >>> [1,2,3].__eq__([2,3,4]) False >>> int(2).__lt__(5) True >>> ‘a’.__le__(‘a’) True >>> [1,1,2,3,5,8].__len__() 6 >>> a = Point(3, 4) >>> a Point(3, 4) Introduction to Computing Using Python Overloading repr() In Python, operators are translated into method calls To add an overloaded operator to a user-defined class, the corresponding method must be implemented >>> a = Point(3, 4) >>> a Point(3, 4) To get this behavior method __repr__()must be implemented and added to class Point class Point: # other Point methods here def __repr__(self): ‘canonical string representation Point(x, y)’ return ‘Point({}, {})’.format(self.x, self.y) __repr__() should return the (canonical) string representation of the point >>> a = Point(3, 4) >>> a.__repr__() Point(3, 4) Introduction to Computing Using Python Overloading operator + To get this behavior method __add__()must be implemented and added to class Point class Point: # other Point methods here def __add__(self, point): return Point(self.x+point.x, self.y+point.y) def __repr__(self): ‘canonical string representation Point(x, y)’ return ‘Point({}, {})’.format(self.x, self.y) >>> a = Point(3,4) >>> b = Point(1,2) >>> a+b Point(4, 6) __add__()should return a new Point object whose coordinates are the sum of the coordinates of a and b >>> a = Point(3,4) >>> b = Point(1,2) >>> a.__add__(b) Point(4, 6) Also, method __repr__() should be implemented to achieve the desired display of the result in the shell >>> a = Point(3,4) >>> b = Point(1,2) >>> a+b Point(4, 6) >>> a = Point(3,4) >>> b = Point(1,2) >>> a.__add__(b) Point(4, 6) >>> print([1,2,3]) [1, 2, 3] >>> print(193) 193 >>> print(set()) set() >>> [1,2,3].__str__() ‘[1, 2, 3]’ >>> int(193).__str__() ‘193’ >>> set().__str__() ‘set()’ Operator Method x + y x.__add__(y) x – y x.__sub__(y) x * y x.__mul__(y) x / y x.__truediv__(y) x // y x.__floordiv__(y) x % y x.__mod__(y) x == y x.__eq__(y) x != y x.__ne__(y) x > y x.__gt__(y) x >= y x.__ge__(y) x < y x.__lt__(y) x <= y x.__le__(y) repr(x) x.__repr__() str(x) x.__str__() len(x) x.__len__() (x) .__init__(x) Introduction to Computing Using Python str() vs repr() >>> str([1,2,3]) ‘[1, 2, 3]’ >>> str(193) ‘193’ >>> str(set()) ‘set()’ Built-in function __str()__ returns the “pretty” string representation of an object • This is the representation printed by the print() statement and is meant to be readable by humans Built-in function __repr()__ returns the canonical string representation of an object • This is the representation printed by the shell when evaluating the object • The string returned by __repr__ method must look like the statement that creates that object Programming exercise 2: Open file lab10.py. It contains the classes we developed during lectures last week. Do the following exercises: Overload appropriate operators for class Card so that you can compare cards based on rank. In particular override __gt__ , __ge__ , __lt__ and __le__ >>> c1=Card(‘3′,’\u2660’) >>> c2=Card(‘5′,’\u2662’) >>> c1 Card(3,♠) >>> c2 Card(5,♢) >>> c1 < c2 True >>> c1 > c2 False >>> c1<=c2 True Programming exercise 3: Bank Account Develop a class BankAccountthat supports these methods: •__init__:Initializes the bank account balance to the value of the input argument, or to 0 if no input argument is given • withdraw: Takes an amount as input and withdraws it from the balance • deposit: Takes an amount as input and adds it to the balance • balance: Returns the balance on the account •__repr__: >>> x = BankAccount(700) >>> x.balance() 700.00 >>> x.withdraw(70) >>> x.balance() 630.00 >>> x.deposit(7) >>> x.balance() 637.00 >>> x BankAccount(637.00) Programming exercise 4: Ping Pong Write a class named PingPong that has a method next that alternates between printing ‘PING’ and ‘PONG’ as shown below. >>> ball = PingPong() >>> ball.next() PING >>> ball.next() PONG >>> ball.next() PING >>> ball.next() PONG Programming exercise 5a: Class Queue Goal: develop a class Queue , an ordered collection of objects that restricts insertions to the rear of the queue and removal from the front of the queue •The class Queue should support methods: • Queue(): Constructor that initializes the queue to an empty queue • enqueue(item): Add item to the end of the queue • dequeue(): Remove and return the element at the front of the queue • isEmpty(): Returns True if the queue is empty, False otherwise >>> appts = Queue() >>> appts.enqueue(‘John’) >>> appts.enqueue(‘Annie’) >>> appts.enqueue(‘Sandy’) >>> appts.dequeue() ‘John’ >>> appts.dequeue() ‘Annie’ >>> appts.dequeue() ‘Sandy’ >>> appts.isEmpty() True rear rear ‘Annie’ ‘Sandy’ Introduction to Computing Using Python by Lj. Perkovic Class Queue: example >>> appts = Queue() >>> appts.enqueue(‘John’) >>> appts.enqueue(‘Annie’) >>> appts.enqueue(‘Sandy’) >>> appts.dequeue() ‘John’ >>> >>> appts = Queue() >>> appts.enqueue(‘John’) >>> appts.enqueue(‘Annie’) >>> appts.enqueue(‘Sandy’) >>> appts.dequeue() ‘John’ >>> appts.dequeue() ‘Annie’ >>> >>> appts = Queue() >>> appts.enqueue(‘John’) >>> appts.enqueue(‘Annie’) >>> appts.enqueue(‘Sandy’) >>> appts.dequeue() ‘John’ >>> appts.dequeue() ‘Annie’ >>> appts.dequeue() ‘Sandy’ >>> >>> appts = Queue() >>> appts.enqueue(‘John’) >>> appts.enqueue(‘Annie’) >>> appts.enqueue(‘Sandy’) >>> appts.dequeue() ‘John’ >>> appts.dequeue() ‘Annie’ >>> appts.dequeue() ‘Sandy’ >>> appts.isEmpty() True appts ‘John’ front rear ‘Annie’ ‘Sandy’ rear rear Programming exercise 5b: Class Queue Make your class Queue user friendly by adding to it __eq__, __repr__ and __len__ Example: >>> q1=Queue() >>> q1.enqueue(‘kiwi’) >>> q1.enqueue(‘apple’) >>> print(q1) >>> print(q1) Queue([‘kiwi’, ‘apple’]) >>> len(q1) 2 >>> q2=Queue() >>> q2.enqueue(‘apple’) >>> q1==q2 False >>> q1.dequeue() ‘kiwi’ >>> q1==q2 True Programming exercise (Inheritance) 6: Class Vector Implement a class Vector that supports the same methods as the class Point we developed in class. In other words it inherits all atributes (data and methods) from class Point. (Revisit class Animal and Bird to see a simple example) The class Vector should also support vector addition and product operations. The addition of two vectors >>> v1 = Vector(1, 3) >>> v2 = Vector(-2, 4) is a new vector whose coordinates are the sum of the corresponding coordinates of v1 and v2: >>> v1 + v2 Vector(-1, 7) The product of v1 and v2 is the sum of the products of the corresponding coordinates: >>> v1 * v2 10 In order for a Vector object to be displayed as Vector(., .) instead of Point(., .),you will need to override method __repr__(). Programming exercise 7a: Class Marsupial Write a class named Marsupialthat can be used as shown below: >>> m=Marsupial(“red”) >>> m.put_in_pouch(‘doll’) >>> m.put_in_pouch(‘firetruck’) >>> m.put_in_pouch(‘kitten’) >>> m.pouch_contents() [‘doll’, ‘firetruck’, ‘kitten’] >>> print(m) I am a red Marsupial. Programming exercise 7b (Inheritance): Class Kangaroo Write a class named Kangaroo as a subclass of Marsupialthat inherits all the attributes of Marsupial and also: •extends the Marsupial __init__ constructor to take, as input, the coordinates x and y of the Kangaroo object, •has methodjump that takes number values dx and dy as input and moves the kangaroo by dx units along the x-axis and by dy units along the y-axis, and •overloads the __str__ operator so it behaves as shown below. >>> k = Kangaroo(“blue”, 0,0) >>> print(k) I am a blue Kangaroo located at coordinates (0,0) >>> k.put_in_pouch(‘doll’) >>> k.put_in_pouch(‘firetruck’) >>> k.put_in_pouch(‘kitten’) >>> k.pouch_contents() [‘doll’, ‘firetruck’, ‘kitten’] >>> k.jump(1,0) >>> k.jump(1,0) >>> k.jump(1,0) >>> print(k) I am a blue Kangaroo located at coordinates (3,0) Programming exercise 8 : Class Points Write a class named Points(that represents points in the plane). The class has a list containing elements that are objects of type Point. __init__ constructor creates an empty list if no input list is given. Otherwise it sets the list to the given list. •has method add(x,y) that adds an object Point with coordinates x and y to points •has method left_most_point that returns the left most point in the set. If there is more than one left most it returns the bottom left most •Has method len and overrides __repr__ >>> a=[Point(1,1), Point(1,2), Point(2,20), Point(1.5, -20)] >>> mypoints=Points(a) >>> mypoints.add(1,-1) >>> mypoints.left_most_point() Point(1,-1) >>> len(mypoints) 5 >>> mypoints Points([Point(1,1), Point(1,2), Point(2,20), Point(1.5,-20),Point(1,-1)])
