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Figure 1 . Output from the script in Listing 1.
Create and print a list [100, 200, 300, 400, 500]Original length is: 5Replace an element Print the modified list[100, 200, [2, 4, 8, 16, 32, 64], 400, 500]Modified length is: 5Extract and display each element in the list100 200[2, 4, 8, 16, 32, 64] 400500 Extract and display eachelement in nested list 24 816 3264

While the code in Listing 1 does some interesting and useful things, it is missing one major component of modern computer programming -- control flow .

Control flow is generally considered to include the following features plus some others that I will get into in future modules:

  • repetition
  • modularity
  • decision logic


Repetition is the ability to cause specified portions of the code to be executed repeatedly under tightly controlled conditions. Repetition almostalways embeds decision logic in some form. This module will introduce you to one of the mechanisms for implementing repetition in Python -- the while loop. Other mechanisms will be discussed in future modules.


Modularity is the ability to subdivide the code into separate reusable units often called functions and methods . The design of functions and methods will be discussed in future modules.

Decision logic

Decision logic is the ability to make decisions on the basis of the program state and to determine which code will be executed as well as when and how itwill be executed. As mentioned above, repetition almost always embeds decision logic in some form. In addition, Python supports a stand-alone decisioncapability -- the if statement, which will be discussed in a future module.

Discussion and sample code

The while loop

The while loop is the most fundamental and the most general of all the repetition mechanisms in most programming languages. Most programminglanguages provide other more specialized looping mechanisms for convenience, and Python is no exception to that rule. However, the fundamental behavior of mostand perhaps all of those more specialized looping mechanisms can be replicated with a properly-configured while loop.

The code in Listing 2 illustrates the use of a while loop. It also illustrates one of the features of lists -- the append method. Finally, it illustrates a decision structure that is embedded in the while loop.

Listing 2 . Use a while loop to manipulate a list.
# Illustrates the use of a while loop to manipulate a list aList = ["a","b","c"]print(aList) count = 0while count<= 5: print(count)aList.append(count) count = count + 1# count += 1 print(aList)

The output produced by this program is shown in Figure 2 .

Figure 2 . Output from the script in Listing 2.
['a', 'b', 'c'] 01 23 45 ['a', 'b', 'c', 0, 1, 2, 3, 4, 5]

Visualization of the program

Figure 3 shows shows a visualization of the program after stepping through several iterations of the while loop. This static image doesn't do justice to the visualization. You really needto run it yourself and step through the program to appreciate it.

Figure 3. Visualization of the program.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
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.
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
for teaching engĺish at school how nano technology help us
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
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?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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