Python Object Orientation Programming

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Questions and Answers

What parameters does the Rectangle constructor initialized with?

width, height, and character

What is the purpose of the calculate_characters method in the Rectangle class?

To calculate the total number of characters in the rectangle

What is the purpose of the str method in the Rectangle class?

To return a string representation of the Rectangle object

How can you check the type of a variable in Python?

Using the type() function or the is keyword Signup and view all the answers

What is the purpose of the draw method in the Rectangle class?

To draw the rectangle with the specified dimensions and character Signup and view all the answers

What is the difference between a class and an object?

A class is a blueprint, while an object is an instance of the class Signup and view all the answers

Can you use built-in classes as base classes for your own classes?

Yes Signup and view all the answers

What is the purpose of a constructor in a class?

To initialize an object with default or specified values Signup and view all the answers

What is the purpose of the `init(self)` method in a class?

To initialize the object variables when a new object is created. Signup and view all the answers

What are instance variables used for in a class?

To define the data that needs to be stored for each object. Signup and view all the answers

What is the benefit of class reuse?

Once a class is defined, it can be reused over and over again in different programs. Signup and view all the answers

What is the purpose of the `str(self)` method in a class?

To convert an object to a string and is called when an object is printed out. Signup and view all the answers

What is the `self` keyword used for in object-oriented programming?

To refer to the current object instance. Signup and view all the answers

What is a class in object-oriented programming?

A blueprint or template for a new data type. Signup and view all the answers

What is an object method in a class?

An operation that can be applied to an object. Signup and view all the answers

What is the difference between a function and a method?

A function is a standalone operation, while a method is defined within a class and acts on a particular object type. Signup and view all the answers

Can an object method be user-defined?

Yes, user-defined methods can be defined in addition to standard methods. Signup and view all the answers

What is polymorphism in object-oriented programming?

Operations can act on more than one type. Signup and view all the answers

What is encapsulation in object-oriented programming?

Everything for an object is defined or enclosed in a class. Signup and view all the answers

What is the purpose of the `init` method in the `Employee` class?

The <code>__init__</code> method is used to initialize the instance variables of the <code>Employee</code> class. Signup and view all the answers

What is the relationship between the `Person` and `Employee` classes?

The <code>Employee</code> class is a subclass of the <code>Person</code> class. Signup and view all the answers

How does the `Employee` class reuse the `Person` class's constructor?

The <code>Employee</code> class calls the <code>Person</code> class's constructor using <code>Person.__init__(self, n, a)</code>. Signup and view all the answers

What is the purpose of the `str` method in the `Employee` class?

The <code>__str__</code> method is used to return a string representation of the <code>Employee</code> object. Signup and view all the answers

What is the relationship between an `Employee` object and a `Person` object?

An <code>Employee</code> object is a <code>Person</code> object. Signup and view all the answers

How does inheritance promote code reuse in the `Employee` class?

Inheritance allows the <code>Employee</code> class to reuse the attributes and methods of the <code>Person</code> class. Signup and view all the answers

What is the purpose of the `employee_number` instance variable in the `Employee` class?

The <code>employee_number</code> instance variable is used to store the employee number of an <code>Employee</code> object. Signup and view all the answers

What is the difference between the `Person` and `Employee` classes?

The <code>Employee</code> class adds an <code>employee_number</code> instance variable and inherits the attributes and methods of the <code>Person</code> class. Signup and view all the answers

Study Notes

Classes and Objects

A class is a template/blueprint for a new data type, defined using the class keyword.
A class contains object methods and object variables.
Object methods define the actions or operations which can be applied to an object.
Object variables define the data/properties which need to be stored for each object.

Constructors

A constructor is a special method that initializes an object when it is created.
The constructor method is named __init__(self) and is called when a new object is created.
The constructor can use default parameters.

Object Methods

Methods are operations that can be applied to an object.
Object methods have self as the first parameter.
There are standard methods using the double underscore naming convention, such as __init__(self) and __str__(self).
User-defined methods can also be defined.

`self` Keyword

The self keyword refers to the current object instance.
self needs to be used explicitly when specifying object methods and variables.

Object Variables

Object variables, also called instance variables, are used to define the data which needs to be stored for each object.
Object variables are prefaced with self.
The constructor __init__(self) is used to initialize the object variables.

`str(self)` Method

The __str__(self) method converts an object to a string and is called when an object is printed out.
The __str__(self) method typically returns the concatenation of the object variables.

Inheritance

Inheritance defines an "is-a" relationship, meaning a sub-class object typically "is-a" super-class object.
Python implements inheritance by specifying the super-class(es) in round brackets after the class name.
The super-class is referenced using the super-class name.

Class Reuse

Once a class is defined, it can be reused over and over again in different programs.
A class should be saved in a filename, and can be reused in different programs.

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