Python creating objects

Question

The essential properties of a Thing are as follows :

The constructor should take in 1 parameter, the name of the Thing.

stone = Thing ('stone ')

owner : an attribute that stores the owner object of the Thing, usually a Person object.

In OOP, we set this attribute to None during initialization when this Thing does not belong to any Person yet (to signify the absence of an object value).

stone . owner

None

is_owned(): returns a boolean value, True if the thing is “owned” and False otherwise.

stone . is_owned ()

False

4.get_owner(): returns the Person object who owns the Thing object.

stone . get_owner ()

None

Implement the class Thing such that it satisfies the above properties and methods.

im not sure what is wrong with my code:

class Thing:
def __init__(self,name):
    self.name=name
    self.owner=None

def is_owned(self):
    return self.owner!=None
def get_owner(self):
    return self.owner

My question: as the question states, when i input stone.owner, i expect to receive an output None. however, there is no output at all. edit: no output received is accepted instead of None. However, is there any way to return None from stone.owner?

I am not sure but, you wanted method is_owned but you have in your code is_owner. Tell please what exactly is wrong, what output you are getting, and what output you would like to get. — jedruniu
– jedruniu, Commented Apr 9, 2017 at 6:55
you missed self in your method, and remember the indentation. — JkShaw
– JkShaw, Commented Apr 9, 2017 at 6:56

sjjhsjjh · Accepted Answer · 2017-04-09 08:17:15Z

2

Here is an answer using a property with getter.

class Thing(object):

        def __init__(self, name):

            self.name = name

            self.owner = None

           

        @property

        def isOwned(self):

            return self.owner is not None

   

    thing = Thing('stone')

   

    print("owner:", thing.owner)

    print("isOwned:", thing.isOwned)

 

    print("Setting owner.")   

    thing.owner = "Silver"

    print("owner:", thing.owner)

    print("isOwned:", thing.isOwned)

Output is like this:

$ python3 ./thingclass.py

owner: None

isOwned: False

Setting owner.

owner: Silver

isOwned: True

answered Apr 9, 2017 at 8:17

sjjhsjjh

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Comments

Raphael Parreira · Accepted Answer · 2017-04-09 07:04:00Z

1

When you are writing python code, you need to care about indentation.
Every function within a class needs self as parameter.

So, your code must be:

class Thing:
    def __init__(self,name):
        self.name=name
        self.owner="None"

    def is_owned(self):
        return self.owner!="None"
    def get_owner(self):
        return self.owner

answered Apr 9, 2017 at 7:04

Raphael Parreira

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2 Comments

AChampion Over a year ago

A bit pedantic but - self as an argument is just a convention it could be called anything. Instance methods receive the instance as a the first parameter (usually called self), classmethods receive the class as the first parameter (usually called cls) and staticmethods receive nothing.

Raphael Parreira Over a year ago

Thank you, @AChampion ! I didn't know that!

cco · Accepted Answer · 2017-04-09 07:18:30Z

1

The reason nothing is printed is most likely that the Python REPL does not print None values.
The current code in the question is better than the accepted answer (except for the indentation) because None is a singular value in Python, while "None" is an ordinary string (which is neither equal to None nor treated as a False value, both of which are true for None).

answered Apr 9, 2017 at 7:18

cco

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