OOP

Question 1

What are objects?

Answer 1

Objects are Python’s abstraction for data. Formally, it is a collection of data and associated behaviors. All data in a Python program is represented by objects or by relations between objects.

Every object has an identity, a type and a value. An object’s identity never changes once it has been created; you may think of it as the object’s address in memory. The ‘is’ operator compares the identity of two objects; the id() function returns an integer representing its identity.

Question 2

What does an object’s type determine?

Answer 2

determines the operations that the object supports (e.g., “does it have a length?”) and also defines the possible values for objects of that type. The type() function returns an object’s type (which is an object itself). Like its identity, an object’s type is also unchangeable.

Question 3

The value of some objects can change. Objects whose value can change are said to be:

Answer 3

mutable

Question 4

objects whose value is unchangeable once they are created are called:

Answer 4

immutable

Question 5

The value of an immutable container object that contains a reference to a mutable object can change when:

Answer 5

the latter’s value is changed; however the container is still considered immutable, because the collection of objects it contains cannot be changed.

Question 6

An object’s mutability is determined by its type; for instance, numbers, strings and tuples are _______ while dictionaries and lists are __________.

Answer 6

immutable

mutable

Question 7

What does it mean to be object oriented?

Answer 7

To be functionally directed toward modeling objects.

Question 8

What is Object oriented analysis?

Answer 8

the process of looking at a problem, system, or task that somebody wants to turn into an application and identifying the objects and interactions between those objects.

Question 9

What is object oriented design?

Answer 9

the process of converting such requirements into an implementation specification. The designer must name the objects, define the behaviors, and formally specify what objects can activate specific behaviors on
other objects. The design stage is all about how things should be done.

Question 10

Define an iterative development model.

Answer 10

In iterative development, a small part of the task is modeled, designed, and programmed, then the program is reviewed and expanded to improve each feature and include new features in a series of short cycles.

Question 11

What’s the difference between an object and a class?

Answer 11

Classes describe objects. They are like blueprints for creating an object. Objects are instances of classes that can be associated with each other. An object instance is a specific object with its own set of data and behaviors.

Question 12

What is UML?

Answer 12

The relationship between classes of objects in an inventory system aka (Unified Modeling Language).
It is used to specify, visualize, modify, construct and document the artifacts of an object-oriented software-intensive system under development.

It offers a standard way to visualize a system’s architectural blueprints, including elements such as activities, actors, business processes, database
schemas, components, programming language statements, and reusable software components.

It combines techniques from data modeling (entity relationship diagrams), business modeling (work flows),
object modeling, and component modeling. It can be used with all processes, throughout the software development life cycle, and across different implementation technologies.

The Unified Modeling Language is a standardized general-purpose modeling language and nowadays is managed as a de facto industry standard by the Object Management Group (OMG). UML includes a set of graphic notation techniques to create visual models of software-intensive systems.

Question 13

What are objects?

Answer 13

Objects are instances of classes that can be associated with each other. An object instance is a specific object with its own set of data and behaviors; Objects are nouns.

Question 14

What is a class?

Answer 14

A blueprint of an object. It defines the specific characteristics that are shared by all instances of an object for that class.

Question 15

What is a class attribute?

Answer 15

It defines the properties of the class. eg. name, weight, height, color, etc. Attributes are adjectives.

Question 16

What is a class method?

Answer 16

The behaviors that can be performed on a specific class of objects.  Methods are like functions in structured programming, but they have access to all the data
associated with that object. Like functions, methods can also accept parameters, and return values.  Methods are verbs.

Question 17

What are parameters to a method?

Answer 17

a list of objects that need to be passed into the method that is being called.

Question 18

What does it mean to invoke a method?

Answer 18

Also known as method call, it is the process of telling the method to execute itself by passing it the required parameters as arguments.

Question 19

Define encapsulation.

Answer 19

The process of hiding the implementation, or functional details, of an object via information hiding. Encapsulation is, literally, creating a capsule, so think of creating a time capsule. If you put a bunch of information into a time capsule, lock and bury it, it is both encapsulated and the information is hidden.

Question 20

What is a model?

Answer 20

An abstraction of a real concept.

Question 21

Define abstraction.

Answer 21

means dealing with the level of detail that is most appropriate to a given task. It is the process of extracting a public interface from the inner details. when abstracting interfaces, try to model exactly what needs to be modeled and nothing more.

Question 22

What should you consider when designing an interface?

Answer 22

When designing the interface, try placing yourself in the object’s shoes and imagine that the object has a strong preference for privacy. Don’t let other objects have access to data about you unless you feel it is in your best interest for them to have it. Don’t give them an interface to force you to perform a specific task unless you are certain you want them to be able to do that to you.

Question 23

Define composition.

Answer 23

The act of collecting together several objects to compose a new one. Composition is usually a good choice when one object is part of another object and that object cannot exist without the primary object.

Question 24

Define object diagram.

Answer 24

also called an instance diagram. It describes the system at a specific state in time, and is describing specific instances of objects, not the interaction between classes.

Question 25

Define aggregation.

Answer 25

Aggregation is almost exactly like composition. The difference is that aggregate objects can exist independently

Question 26

Define inheritance.

Answer 26

one class can inherit attributes and methods from another class.

Question 27

Define polymorphism

Answer 27

is the ability to treat a class differently depending on which subclass is implemented.

Question 28

Define multiple inheritance.

Answer 28

allows a subclass to inherit functionality from multiple parent classes.

Question 29

Define asynchronous message.

Answer 29

typically means the first object calls a method on the second object which returns immediately.

Question 30

Define refactoring.

Answer 30

improve the design by moving code around, removing duplicate code or complex relationships in favor of simpler, more elegant designs.

Question 31

When is inheritance most useful?

Answer 31

when the subclasses have some kind of specialization. Specialization is creating or changing attributes or behaviors on the subclass to make it somehow different from the parent class.

Question 32

What is a primitive data type?

Answer 32

A variable of a primitive type directly contains the value of that type (in other words, they are value types).

A variable of a non-primitive type doesn’t contain the value directly; instead, it is a reference (similar to a pointer) to an object. (It is not possible in Java to create user-defined value types).

Question 33

What is a use case model?

Answer 33

A representation of the systems we intend to model along with its intended functions and environment drawn as a diagram. It names the actors and gives the heading for each scene. Use case models have no timely order.

Question 34

What is a class diagram?

Answer 34

For object-oriented software engineers, the Class diagram is the most important one. A Class diagram consists of classes and lines between them. The classes
themselves are drawn as boxes, having two compartments, one for methods and one for
attributes.

Question 35

What are the 3 relationships between objects?

Answer 35

~ association
~ aggregation
~ inheritance

Question 36

Define association.

Answer 36

a static relationship, usually one class is attribute of another class, or one class uses
another class

Question 37

Define aggregation.

Answer 37

for instance an order consists of order details

Question 38

Define inheritance.

Answer 38

describes a hierarchy between classes

Question 39

What is a diagram?

Answer 39

a partial graphic representation of a system’s model.

Question 40

What are the two different views of a system model that UML diagrams represent?

Answer 40

Static (or structural) view: emphasizes the static structure of the system using objects, attributes, operations
and relationships. The structural view includes class diagrams and composite structure diagrams.

Dynamic (or behavioral) view: emphasizes the dynamic behavior of the system by showing collaborations
among objects and changes to the internal states of objects. This view includes sequence diagrams, activity
diagrams and state machine diagrams.

Question 41

In UML there are 14 types of diagrams divided into 2 categories. What are they?

Answer 41

Seven diagram types represent
structural information, and the other seven represent general types of behavior, including four that represent
different aspects of interactions. These diagrams can be categorized hierarchically as shown in the following
diagram:

Question 42

Define Class diagram:

Answer 42

describes the structure of a system by showing the system’s classes, their attributes, and the
relationships among the classes.

Question 43

Define Component diagram:

Answer 43

describes how a software system is split up into components and shows the dependencies
among these components.

Question 44

Define Composite structure diagram:

Answer 44

describes the internal structure of a class and the collaborations that this structure makes possible.

Question 45

Define Deployment diagram:

Answer 45

describes the hardware used in system implementations and the execution environments and artifacts deployed on the hardware.

Question 46

Define Object diagram:

Answer 46

shows a complete or partial view of the structure of a modeled system at a specific time.

Question 47

Define Package diagram:

Answer 47

describes how a system is split up into logical groupings by showing the dependencies among these groupings.

Question 48

Define Profile diagram:

Answer 48

operates at the metamodel level to show stereotypes as classes with the <> stereotype, and profiles as packages with the <> stereotype. The extension relation (solid line with closed, filled arrowhead) indicates what metamodel element a given stereotype is extending.

Question 49

Define Use case diagram:

Answer 49

describes the functionality provided by a system in terms of actors, their goals represented as use cases, and any dependencies among those use cases.

Question 50

Define Activity diagram:

Answer 50

describes the business and operational step-by-step workflows of components in a system. An activity diagram shows the overall flow of control.

Question 51

Define state machine diagram:

Answer 51

describes the states and state transitions of the system.

Question 52

Define Sequence diagram:

Answer 52

shows how objects communicate with each other in terms of a sequence of messages. Also indicates the lifespans of objects relative to those messages.

Question 53

Define Communication diagram:

Answer 53

shows the interactions between objects or parts in terms of sequenced messages. They represent a combination of information taken from Class, Sequence, and Use Case Diagrams describing both the static structure and dynamic behavior of a system.

Question 54

Define Interaction overview diagram:

Answer 54

provides an overview in which the nodes represent communication diagrams.

Question 55

Define Timing diagrams:

Answer 55

a specific type of interaction diagram where the focus is on timing constraints.

Question 56

How do you create a class in Python that doesn’t do anything?

Answer 56

class MyFirstClass:
         pass

Question 57

What is considered to be Python’s delimiter?

Answer 57

tab or 4 spaces

Question 58

Can you instantiate a class that does nothing?

Answer 58

yes

Question 59

Define dot notation

Answer 59

When you assign a value to an attribute on an object and use the syntax . = . The value can be anything: a Python primitive, a
built-in data type, another object. It can even be a function or another class!

Question 60

How do you give a class that does nothing attributes?

Answer 60

We can set arbitrary attributes on an instantiated object using the dot notation:
class Point:
        pass
p1 = Point()
p2 = Point()
p1.x = 5
p1.y = 4
p2.x = 3
p2.y = 6
print(p1.x, p1.y)
print(p2.x, p2.y)

Question 61

A method in python is identical to?

Answer 61

defining a function. essentially, the method really is just a function that happens to be on a class.

Question 62

How do you start a method?

Answer 62

It starts with the keyword def followed by a space and the name of the method. This is followed by a set of parentheses containing the parameter list, and terminated with a colon. The next line is indented to contain the statements inside the method. These statements can be arbitrary Python code operating on the object itself and any parameters passed in as the method sees fit.

Question 63

What’s the difference between methods and normal functions?

Answer 63

all methods have one required argument. This argument is conventionally named self;

Question 64

What is the self argument?

Answer 64

a reference to the object that the method is being invoked on.

Question 65

How do you pass multiple arguments to a method?

Answer 65

class Point:
        def move(self, x, y):
               self.x = x
               self.y = y

        def reset(self):
               self.move(0, 0)

        def calculate_distance(self, other_point):
               return math.sqrt(
                         (self.x - other_point.x)**2 +
                         (self.y - other_point.y)**2)

Question 66

How do you call the methods

Answer 66

how to use it:

point1 = Point()
point2 = Point()

point1. reset()
point2. move(5,0)

print(point2.calculate_distance(point1))
assert (point2.calculate_distance(point1) ==
point1.calculate_distance(point2))
point1.move(3,4)
print(point1.calculate_distance(point2))
print(point1.calculate_distance(point1))

Question 67

Most object-oriented programming languages have the concept of a constructor. Define constructor.
How is python different?

Answer 67

a special method that creates and initializes the object when it is created.
Python is a little different; it has a constructor and an initializer.

Question 68

What is python’s initialization method?

Answer 68

__init__
this is a special method that the Python interpreter will treat as a special case. The __init__ method requires the user to supply arguments when an object is instantiated.

Question 69

What are python modules?

What happens when we have more than 1 python file in a folder?

Answer 69

modules are simply python files and nothing more.
The single file in our small program is a module. Two Python files are two modules. If we have two files in the same folder, we can load a class from one module for use in the other module.

Question 70

What is the import statement used for?

Answer 70

importing modules or specific classes or functions from modules.

Question 71

What are several ways to import modules?

Answer 71

import database
db = database.Database()
This version imports the database module into the products namespace (the list of names currently accessible in a module or function), so any class or function in the database module can be accessed using database. notation.
________________________
or
Alternatively, we can import just the one class we need using the from…import syntax:

from database import Database
db = Database()
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
or
If, for some reason, products already has a class called Database, and we don't want the two names to be confused, we can rename the class when used inside the products module:

from database import Database as DB
db = DB()
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
or
We can also import multiple items in one statement. If our database module also contains a Query class, we can import both classes using:

from database import Database, Query
or all classes using:

from database import *
****Bear in mind that using the import * syntax can bring unexpected objects into our local namespace. Sure, it will import all the classes and functions defined in the module being imported from, but it will also import any classes or modules that were themselves imported into that file!****

There should be no magic variables that seem to come out of thin air. We should always be able to immediately identify where the names in our current namespace originated.

Question 72

Define a package.

Answer 72

a collection of modules in a folder. The name of the package is the name of the folder. All we need to do to tell Python that a folder is a package and place a (normally empty) file in the folder named __init__.py. If we forget this file, we won’t be able to import modules from that folder.

Question 73

Define absolute imports.

Answer 73

the complete path to the module, function, or path we want to import. If we need access to the Product class inside the products module, we could use any of these syntaxes to do an absolute import:
import ecommerce.products
product = ecommerce.products.Product()
or
from ecommerce.products import Product
product = Product()
or
from ecommerce import products
product = products.Product()

Question 74

Define relative imports.

Answer 74

Relative imports are basically a way of saying "find a class, function, or module as it is positioned relative to the current module". For example, if we are working in the products module and we want to import the Database class from the database module "next" to it, we could use a relative import:
from .database import Database

The period in front of database says, “Use the database module inside the current package”.

Question 75

How do we access a parent package?

Answer 75

That is easily done with two periods:
from ..database import Database

We can use more periods to go further up the hierarchy.