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Creating Classes

Look the code below. It defines a class. it also declares methods which are functions that are defined inside of a class. One of the methods, __init__, is automatically called when a new object is created by the class. One of the methods, __str__, is automatically called when you print an object of the class.

A Book Class

Run the following code

class Book: """ Represents a book object """ def __init__(self, title, author): self.title = title self.author = author def __str__(self): return "title: " + self.title + " author: " + self.author def main(): b2 = Book("A Wrinkle in Time", "M. L'Engle") print(b2) b1 = Book("Goodnight Moon", "Margaret Wise Brown") print(b1) main()

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Creating More Objects

Once you have defined a class you can use it to create many objects.

Change the following main function to add a person object with your first and last name.

class Person: """ Represents a person object """ def __init__(self, first, last): self.first = first self.last = last def __str__(self): return self.first + " " + self.last def main(): p1 = Person("Barbara", "Ericson") print(p1) main()

Add a Method to a Class

You can add a new method to a class by adding a new function inside the class. For example, you can add the initials method to the Person class. The function must take an object of the class to work with that by convention we call self. The name of the function doesn’t need to have any underscores in it.

Change the following Person class to add an initials method that returns a string with the first letter in the first name and the first letter in the last name in lowercase.

class Person: """ Represents a person object """ def __init__(self, first, last): self.first = first self.last = last def __str__(self): return self.first + " " + self.last def main(): p1 = Person("Barbara", "Ericson") print(p1) print(p1.initials()) main() ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): p1 = Person("Barbara", "Ericson") self.assertEqual(p1.initials(),'be',"testing initials for Barbara Ericson") p2 = Person("Enoch", "Obe") self.assertEqual(p2.initials(),"eo", "testing initials for Enoch Obe") myTests().main()

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Click on the following link to go the practice problems: Practice Problems

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