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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

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
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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