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A practical example

Many years ago when I did a tour of duty as an enlisted man in the U.S. Air Force, the drill sergeant had a habit of lining us up and telling us to "count off."

What that meant was that the first person in the line called out the number one , the person behind him called out the number two , the person behind him called out the number three , etc.

(Since learning about computer programming, I now wonder if the first person should have called out zero. I notice that thefirst case of Ebola in the United States is being identified by the CDC as case 0.)

Assigning an ordinal index

I'm sure the drill sergeant didn't realize that what he was doing was assigning an ordinal index value to each person in the line (and neither did I realize it at the time) .

Using an ordinal index

Even though he didn't know the technical details of ordinal indices, he didn't have any difficulty yelling, "Number six, wash dishes, number fourteen,peel potatoes, number twenty-two, carry out the garbage, etc."

That is what using an index is all about -- using an ordinal index to select an item. As you will see in a future module titled Itse1359-1080-Lists Part 1 , this is also referred to as a subscription in Python. In the context of this module, indexing is the process of assigning an ordinal index value to each data item contained in some sort of acontainer.

In other words, we assign an ordinal number to each item, which describes the numerical position of the item in the container.

A dozen eggs:

For example, if you were very careful, you could use a felt tip pen to assign an ordinal index to each of the twelve eggs contained in acarton containing a dozen eggs. (Should you start with zero or one?)

Then you could extract the egg whose index value is 9 from the container and eat it for breakfast.

Having assigned the index, we can use that index to access the data item corresponding to that index, as in "Number six, wash dishes."

Index values automatically assigned

In this module, we will be using the index values that are automatically assigned to the characters in a string for the purpose of accessing thosecharacters, both individually, and in groups.

Slicing

Here is what Magnus Lie Hetland has to say on the topic of slicing (and indexing as well.) Although this quotation was taken from a discussion of lists, it applies equallywell to strings. (Note that some material was deleted from the quotation for brevity.)

According to Magnus Lie Hetland:

"One of the nice things about lists is that you can access their elements separately or in groups, through indexing and slicing.

Indexing is done (as in many other languages) by appending the index in brackets to the list. (Note that the first element has index 0) ...

(This is the answer to the question about the first egg -- Baldwin)

Slicing is almost like indexing, except that you indicate both the start and stop index of the result, with a colon (":") separating them: ...

Notice that the end is non-inclusive. If one of the indices is dropped, it is assumed that you want everything in that direction. i.e. list[:3]means "every element from the beginning of list up to element 3,non-inclusive." ...

list[3:] would, on the other hand, mean "everyelement from list, starting at element 3 (inclusive) up to, and including, the last one."

For really interesting results, you can use negative numbers too: list[-3]is the third element from the end of the list..."

Questions & Answers

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
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 ?
s.
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
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
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
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
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
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit 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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