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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

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

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

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
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
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
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
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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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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