# 1.5 Itse1359-1030-variables and identifiers  (Page 6/7)

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Figure 5 . Python takes care of routine type issues automatically.
```>>>x=5>>>y=6>>>x+y 11>>>x=5.55555>>>y=6.66666>>>x+y 12.22221>>>```

## Assign some floating point values

Following that, the floating point values 5.55555 and 6.66666 are assigned to the same two variables named x and y. The two variables are successfullyadded and the correct result is displayed, demonstrating that the two floating point values were successfully stored in the variables originally created forintegers.

## How is this accomplished?

I don't know the inner workings of exactly how this is accomplished. As Python programmers, we don't usuallycare. We are simply happy that it works without the requirement for us to deal with the details of type.

## The magic continuation variable

In interactive mode, Python automatically provides a variable whose name is simply the underscore character (_).

This variable makes it easy to do continuation arithmetic in interactive mode. (This variable is intended for read only purposes, so don't assign a value to it explicitly.)

At any point in time in interactive mode, this variable will contain the most recent output value displayed by the interpreter.

## How does it work ?

Consider the interactive code fragment shown in Figure 6 . This fragment starts out just like previous examples, causing the sum of 5 and 6 to be calculated anddisplayed.

Figure 6 . The magic continuation variable.
```>>>5+6 11>>>_+22 # add 22 to the continuation variable 33>>>```

## Sum is saved in the continuation variable

As mentioned above, the sum value of 11 is automatically saved in the continuation variable whose name is simply the underscore.

The contents of the continuation variable (11) are then added to 22 producing a result of 33. (Note the use of the underscore as the left operand of the addition operator.)

## The primary purpose of the continuation variable

The primary purpose of this automatic variable named _ is to make it easier for you to string calculations together in interactive mode and todisplay the intermediate results as you go.

## Illegal variable names

The interactive fragment in Figure 7 shows the result of attempting to use an illegal variable name.

Figure 7 . An illegal variable name.
```>>>1x=6 SyntaxError: invalid syntax>>>```

The output shown in Figure 7 was produced by the IDLE GUI interface. Although not shown here, the "1x" was highlighted with a red background. (The command-line interface provides essentially the same information but in a different format.)

Variable names cannot begin with a digit. They must begin with either a letter or an underscore character. That was the reason for the error in Figure 7 . (Without getting into the details as to why, I recommend that you never begin a variable name or a method name with the underscore character.)

## Variable name spelling errors

The interpreter assumes that you know what you are doing, and won't help you avoid spelling errors in variable names (unless the spelling error produces an illegal variable name) .

## A serious programming problem

Now I will illustrate a very subtle and very serious programming problem. Consider the interactive code fragment in Figure 8 . The programmer expected to get a final answer of 16+5 = 21, but instead thefinal answer was 11.

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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 ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
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
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
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