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Program output

The output from this program is shown in Figure 1 .

Figure 1 . Program output.
Print index value 2 A stringPrint a short slice [3.14, 59, 'A string']Print the entire list [3.14, 59, 'A string', 1024]

Visualize sliced lists

Create new lists by slicing an existing list

Figure 2 shows the output from the code visualizer for code similar to the code in Listing 4 . Instead of accessing the list elements and printing them on the fly as in Listing 4 , the code in Figure 2 accesses the list elements and saves references to them so that we can see what the resulting lists look like.

Figure 2. Visualize sliced lists.

Visualize sliced lists.

The diagram on the right in Figure 2 shows the state of the program in memory following the execution of all the code in the code box on the left. Asyou can see, there are now three separate lists:

  • the original list pointed to by the variable named theList and
  • two new lists pointed to by bList and cList .

The two new lists were created by slicing the original list. The elements in the lists allpoint to the float , int , and str objects that were used to populate the original list.

Figure 2 illustrates a very important concept. Three of the variables shown in the light blue box point to objects of type list. Theelements that populate those list objects point to other objects of the types float , int , and str (This concept is often called indirection.)

Since the two bottom lists were created as slices of the original (top) list, they all point to the same objects at this stage in the execution of theprogram.

Change an item in the original list

Figure 3 shows what happens when one of the elements of the original list object is modified to cause it to point to a different object. (Note the arrow that now points from element 2 in the original list object down the screen to a new str object containing the word "changed" .)

Figure 3. Change an item in the original list.

Change an item in the original list.

The important thing to note here is that the pointers in element 2 in the other twolist objects did not follow suite. In other words, they still point to the original str object containing the words "A string" and they do not point to the new str object containing the word "changed" . Thus, even though the two new list objects werecreated as slices from the original list object, once they are created, they are not dependent on thecontents of the original list object. Subsequent changes in the contents of the original list object are not reflected in the contents of the two newlist objects.

Lists can be concatenated

Lists can be concatenated using the + operator.

A concatenation program

The Python program shown in Listing 5 creates two lists and prints them both. Then it concatenates the two lists and prints the concatenated version.

Listing 5 . Lists can be concatenated.
# Illustrates concatenating lists ##------------------------------- print("Create two lists")listA = [3.14,59,"A string",1024] listB = [2,4,6,16]print("Print listA") print(listA)print("Print listB") print(listB)print("Concatenate the lists") listC = listA + listBprint("Print concatenated list") print(listC)

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris 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
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
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele 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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