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Main Page → Exercises → Python → Solve an Exercise

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Language/Type: Python recursion

Answer the following questions about classes and objects:

What is an object?
An object is when a program crashes with an error. A function that calls itself. An entity that combines state and behavior. Any value in a program such as an int or string. An object is a synonym for a program. (order shuffled)
How is an object different from a class?
A class is a template or blueprint for a new type, and an object is an instance of that type. An object is larger and more powerful than a class. They are the same; the terms are interchangeable. Python supports objects but does not support classes. Objects can only store data, while classes can also contain behavior (methods). (order shuffled)
What is the difference between object-oriented programming and procedural programming?
Object-oriented programming contains no simple values like ints, only objects. Object-oriented programming is more powerful and able to solve more problems than procedural. Python is a procedural language and does not allow object-oriented programming. Procedural programs runs code in sequential order, while object-oriented programs run in random orders chosen by the objects. Procedural programming treats a program as a sequence of actions or commands, and object-oriented programming looks at a program as a group of interacting objects. (order shuffled)
What is the difference between a parameter and a data attribute?
Parameters use less memory than data attributes. Parameters use a different syntax where you must specify a default value. Parameters are one type of data attribute. The other is a list. When making a class, data attributes are optional but parameters are required. An attribute is stored inside of an object, while a parameter is passed in to a function. (order shuffled)
What is the difference between an accessor and mutator method?
An accessor provides access to an object's data, while a mutator changes the object's state. An accessor requires that the caller request access before calling it. A mutator converts one type of object into another type of object. Accessors are normal methods (functions) and mutators are ones that are part of objects. Accessors are public while mutators are private. (order shuffled)
Suppose we have a class BankAccount with a method compute_interest(self, rate). What is the correct syntax to call this method on a variable named acct?
result = compute_interest(acct, 42) acct.compute_interest(42.0, 15) result = BankAccount.compute_interest(42) result = acct.compute_interest(42) BankAccount(42).compute_interest()
How do you write a class whose objects can easily be printed on the console?
Write a print method in the class. Write a __str__ method in the class. Use only data attributes of type string in the class. Comment the class thoroughly. Include a bool attribute, printable = True.
The following print statement is equivalent to which of the following? d1 = Date() ... print(d1)
print(__str__(d1)) d1.__str__() print(d1.__str__()) print(Date.__str__())
What is abstraction?
Writing pseudocode without implementing the actual program. Declaring a method's heading but omitting the body of the method. Multiple classes providing the same functionality. The ability to focus on a problem at a high level without worrying about the minor details. Writing object-oriented code rather than procedural code. (order shuffled)
How do objects provide abstraction?
Objects do not provide abstraction if the client can see their source code. By linking data and behavior without having to manage and manipulate the data directly. Methods are more secure than normal functions. They force us to split our programs into multiple files. The improved performance from objects makes programs faster, which makes them more abstract. (order shuffled)
When attributes are made private, client programs are not supposed to access them directly. How do you allow classes access to read these attributes' values, without letting the client break the object's encapsulation?
Raise an error that contains the object's state. Create properties that return their values. Write the object's state out to a file, and let the client read from the file. Print the object's state to the console. Just let the client access the data attributes directly, since they are not actually private. (order shuffled)
How does encapsulation make it easier to change the internal implementation of a class?
Encapsulation makes the class invisible to clients, so they cannot use it at all. Clients do not directly access the attributes, so changing those fields will not disturb client behavior as long as the external view (method behavior) is consistent. Encapsulated objects tend to be better documented, so if there is a change, the client will see it in the documentation and know to change their code. Encapsulated objects do not have any data attributes, so there is no implementation to change. Encapsulation allows you to call the change_implementation() method on the object. (order shuffled)
How can you tell whether a class is cohesive?
When each of its attributes stores important state related to the object and each method interacts with that state in some way to produce useful behavior. When it has high performance and runs quickly. When it has thorough documentation and comments. When it runs well in a text interface and/or graphical user interface. When it does not contain very many attributes or methods. (order shuffled)
Why is it often considered poor style to put console I/O code into a class?
It can cause errors to be raised from the class's code. It makes the class have poor runtime performance. We cannot put I/O code in a class because the print() function does not have access to the 'self' parameter. Doing so forces clients to use a text interface with that class and forces them to use exactly the same messages in that interface. (order shuffled)

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Main Page → Exercises → Python → Solve an Exercise

class_concepts