<< Chapter < Page Chapter >> Page >

A sample program

I will illustrate indexing and slicing of strings using a sample program contained in a script file named String01.py .

The program listing

A complete listing of the program, (along with the output produced by the program) , is provided in Listing 9 near the end of the module.

Will discuss in fragments

I will discuss the program in fragments, illustrating particular aspects of indexing and slicing in each fragment. This is a scheme that I will usefrequently in this set of tutorial modules.

Interesting code fragments

Extract a single character

A single character can be extracted from a string by referring to the string and enclosing the index of the character in square brackets, as shown in thecode fragment in Listing 1 .

Listing 1 . Extract a single character.
aStr = "This is a string" print(aStr[0]) #print T print(aStr[3]) #print s

(Note that this is a fragment from a script file, not from an interactive Python program.)

Create a string object to work with

The fragment in Listing 1 creates a string object and assigns it to a variable named aStr . From this point forward, the contents of the string can be accessed by referring to the variable.

Visualizing the string object

Figure 1 shows a visualization of the string object. This visualization was produced using the Online Python Tutor .

Figure 1. Visualizing the string object.

missing image

The green arrow in Figure 1 indicates that the first statement in the program is the most recently executed statement in this visualization. (This is the statement that created the string object.) The diagram on the right shows that the variable named aStr contains a reference to an object of type str , which contains the value: "This is a string" .

This is a very simple diagram but it shows a pattern that you need to remember. Variables in Python containreferences to objects. Those objects may be "dumb" objects intended solely to encapsulate a value (such as type int ) or they may be "smart" objects (such as type str ) that can not only encapsulate data values but can also encapsulate methods (such as capitalize() ) to manipulate those data values in various ways.

(Note that even the dumb objects are not completely dumb. For example,all of the numeric types such as int know how to participate in arithmetic operations, how to negate themselves, and how to do a few otherthings that might be expected of a numeric.)

Index values always begin with zero

Unlike eggs and Air Force enlisted men, the first character in a string is always located at index 0, as in aStr[0] .

Thus, the second statement in the fragment extracts and prints the T , which is the first character in the word This .

Display the character at index 3

Similarly, the last statement in the fragment in Listing 1 extracts and prints the s from index position 3, as in aStr[3] . The character at this index position is the s that ends the word This .

The last statement is equivalent to the following request, "Will the character at index position 3 please display yourself on the screen."

Is this the fourth character ?

You would probably refer to this as the fourth character, and you would be correct if you did. The character at index 3 is the fourth character in thestring. The character at index 0 is the first character in the string. First does not equate to index 1. You need to think about this, because this can be avery confusing topic for new programmers.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
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?