# 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.

where we get a research paper on Nano chemistry....?
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
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
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
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?
what is a peer
What is meant by 'nano scale'?
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
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
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?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
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