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If a parameter is passed by reference, the incoming parameter can be used by code in the function to modify the original. Some programming languages supportboth types of parameter passing.

According to tutorialspoint -- Python Functions , all parameters in Python are passed by reference . On the other hand, according to The Python Tutorial -- Defining Functions ,

"thus, arguments are passed using call by value (where the value is always an object reference, not the value of the object)."

In this case, I come down on the side of call by value . I think it is more correct to say that parameters are passed by value and as a result, thefunction receives copies of references to objects. Even though I can use a copy of an object's reference to modify the object, I cannot use a copy of thatreference to cause the original reference to point to a different object. I can modify the object to which the reference points, but I cannot modify thereference itself.

I will illustrate what I mean by this in conjunction with the program in Listing 1 .

Discussion and sample code

This module will examine the following kinds of arguments:

  • Required arguments
  • Default arguments
  • Keyword arguments
  • Variable-length arguments

Passing by value or reference

The program shown in Listing 1 illustrates the significance of passing parameters by value or by reference when those parameters are references to objects. Listing 1 also illustrates the use of two required arguments .

Listing 1 . A list-modifier function.
# Illustrates pass by value or reference #---------------------------------------------------def listModifier(listA,listB): """Illustrates pass by value or reference"""print("In listModifier") print("Use incoming parameter to append to listA")listA.append(3.14159) print("New listA = " + str(listA))print("Assign a new list to listB") listB = ["A","new","list"]print("New listB = " + str(listB)) return#End function definition #Call the functionprint("Create two lists") aList = ["ab","cd","ef"]bList = ["The","old","list"] print("aList = " + str(aList))print("bList = " + str(bList)) print("Call listModifier")listModifier(aList,bList) print("Back from listModifier")print("aList = " + str(aList)) print("bList = " + str(bList))

Figure 1 shows the output produced by the code in Listing 1 .

Figure 1 . Output from the code in Listing 1.
Create two lists aList = ['ab', 'cd', 'ef']bList = ['The', 'old', 'list'] Call listModifierIn listModifier Use incoming parameter to append to listANew listA = ['ab', 'cd', 'ef', 3.14159] Assign a new list to listBNew listB = ['A', 'new', 'list'] Back from listModifieraList = ['ab', 'cd', 'ef', 3.14159] bList = ['The', 'old', 'list']

The function definition

The code in Listing 1 defines a function named listModifier . This function receives two incoming parameters. Each parameter points to adifferent list. I contend that the incoming parameters are actually copies of the variables that were passed as parameters.

The code in the function uses one of the incoming parameters to access the list and to append a value of 3.14159 onto the end of the list. The second line of text from the bottom of Figure 1 confirms that this operation was successful.

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
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
what is the stm
Brian Reply
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?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
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
what is Nano technology ?
Bob Reply
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?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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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