<< Chapter < Page Chapter >> Page >
Figure 6 . Output from the code in Listing 10.
6 Modify class var using class 7 Display class var using objectsTestClass object at 0x02091DD0: [1, 2, 3, 4, 'a', True] TestClass object at 0x0218C710: [1, 2, 3, 4, 'a', True]8 Display class var using class: [1, 2, 3, 4, 'a', True]

Both objects see the change that was made to the list even though that change was made independently of either object.

A word of caution is in order

This sort of behavior can lead to programming errors that are very easy to make and very difficult to find and fix. In my opinion, you should usemutable class variables very rarely if at all. On the other hand, class variables that are not mutable, such as tuples, can be very useful and are muchsafer to use. Even in that case, however, one immutable object can be replaced by a different immutable object so even the use of immutable objects is nottotally safe.

Shadowing or hiding a class variable

If an instance variable belonging to an object has the same name as a class variable in the class from which the object was instantiated, the instancevariable will "shadow" or hide the class variable insofar as that object is concerned. This is illustrated by the program shown in Listing 17 . The output from the program is shown in Figure 12 .

Class definition with a shadowing method

The class definition in Listing 11 contains a class variable named classVar . The class definition also contains a method named shadowClassVariable . If that method is executed on an object instantiated from the class, it will add a new instance variable to the objectnamed classVar . From that point forward, the class variable named classVar won't be visible insofar as that object is concerned unless it accesses the class variable using the name of the class, TestClass .

Listing 11 . Class definition with a shadowing method.
class TestClass(object): classVar = 1234#Note, the following code adds a new instance variable named classVar # to the object, which "shadows" or hides the actual class variable# named classVar insofar as this object is concerned. def shadowClassVariable(self):self.classVar = "ABCD" def printClassVar(self):print(str(self)[10:40] + ": " + str(self.classVar))

Listing 11 also defines a method named printClassVar . This method concatenates and prints a portion of the object identifier (self) with the contents of classVar (as seen by the object) .

Instantiate and display classVar in two objects

The code in Listing 12 instantiates two different objects from the class named TestClass and saves the objects' references in the variables named ref01 and ref02 .

Listing 12 . Instantiate and display classVar in two objects.
print("1 Instantiate two objects") ref01 = TestClass()ref02 = TestClass() print("2 Display classVar using objects")ref01.printClassVar() ref02.printClassVar()

The code in Listing 12 also uses those references to call the method named printClassVar on each object. This causes the contents of classVar to be printed as seen by each object at this point in the program. The results are shown in Figure 7 .

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Itse 1359 introduction to scripting languages: python' conversation and receive update notifications?

Ask