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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.


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

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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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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