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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

Ayele, K., 2003. Introductory Economics, 3rd ed., Addis Ababa.
Widad Reply
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Ariel
?
Ariel
What is economics
Widad Reply
the study of how humans make choices under conditions of scarcity
AI-Robot
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn Reply
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn
what is ecnomics
Jan Reply
this is the study of how the society manages it's scarce resources
Belonwu
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macroeconomic is the branch of economics which studies actions, scale, activities and behaviour of the aggregate economy as a whole.
husaini
etc
husaini
difference between firm and industry
husaini Reply
what's the difference between a firm and an industry
Abdul
firm is the unit which transform inputs to output where as industry contain combination of firms with similar production 😅😅
Abdulraufu
Suppose the demand function that a firm faces shifted from Qd  120 3P to Qd  90  3P and the supply function has shifted from QS  20  2P to QS 10  2P . a) Find the effect of this change on price and quantity. b) Which of the changes in demand and supply is higher?
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factors influencing supply
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what is economic.
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Jan
economics is a science that studies human behaviour as a relationship b/w ends and scares means which have alternative uses
Jan
calculate the profit maximizing for demand and supply
Zarshad Reply
Why qualify 28 supplies
Milan
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Nomsa Reply
out-of-pocket costs for a firm, for example, payments for wages and salaries, rent, or materials
AI-Robot
concepts of supply in microeconomics
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economic overview notes
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identify a demand and a supply curve
Salome Reply
i don't know
Parul
there's a difference
Aryan
Demand curve shows that how supply and others conditions affect on demand of a particular thing and what percent demand increase whith increase of supply of goods
Israr
Hi Sir please how do u calculate Cross elastic demand and income elastic demand?
Abari
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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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