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Would be almost worthless in Java or C++

Although it would be technically possible to define an empty class and instantiate objects from that class in Java and C++, such objects probablywouldn't be very useful in their own right.

In Python, you can define an empty class and instantiate objects from that class. You can add instance variables to the object at runtime after itis instantiated, which might be useful in some situations. As you will see in a future module, you can even add class variables to a class after it has beenused to instantiate objects. That might also be useful in some situations.

Add an instance variable to one object

The code in Listing 2 uses the variable named ref01 to add a new variable with a value of 1234 to the object referred to by ref01 .

Listing 2 . Add an instance variable to one object.
print("Add an instance variable to one object and display it") ref01.iVar = 1234print(ref01.iVar)

Listing 2 also uses the reference variable named ref01 to print the value of the new variable belonging to the object referred toby ref01 . Figure 2 shows the output produced by the code in Listing 2 .

Figure 2 . Output from the code in Listing 2.
Add an instance variable to one object and display it 1234

Try to display the same instance variable in the other object

The code in Listing 3 uses the variable named ref02 in an attempt to display the same instance variable on the object referred to by ref02 .

Listing 3 . Try to display the same instance variable in the other object.
print("Try to display the same instance variable in the other object") print(ref02.iVar)

However, the code that added a new instance variable to one object in Listing 2 did not add the same instance variable to both objects that were originally instantiated from the same class. Therefore, at this point, thetwo objects have different structures. The code in Listing 3 produced the error message shown in Figure 3 .

Figure 3 . Output from the code in Listing 3.
Try to display the same instance variable in the other object Traceback (most recent call last):File "1359-1430-13.py", line 18, in<module>print(ref02.iVar) AttributeError: 'TestClass' object has no attribute 'iVar'

Visualize the code in Listing 9

I recommend that you create a visualization for the code in Listing 9 and step through the program one instruction at a time. As you do that, pay attention tothe movements of the red and green arrows on the left, the diagram on the right, and the printed material at the bottom. That should help you to betterunderstand the behavior of empty objects in Python.

Object can modify itself at runtime

The next program that I will discuss is a minor modification to the previous program but ends up with the same result. A complete listing of the program isprovided in Listing 10 and the output from the program is shown in Figure 6 . I will only discuss those things that are different between this program and theprevious program.

The definition of a class named TestClass

The first difference is shown in Listing 4 , which shows the definition of a class named TestClass . Instead of being empty as in the previous program, this class provides a method named addInstanceVar by which an object can add and initialize a new instance variable named iVar to itself at runtime.

Questions & Answers

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Itse 1359 introduction to scripting languages: python. OpenStax CNX. Jan 22, 2016 Download for free at https://legacy.cnx.org/content/col11713/1.32
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