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Chapter 9List

Slides sold at copy shop

ITS100: Introduction to Computer and Programming1

Topics

1. Values and Types2. Lists and List type3. Operations on lists4. Lists in use and Problem solving

variables

statements

functions

data

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Values vs Types

• We have written programs using such entities as 4, 4.0; True, False; “hello”, “world”

• They are data values (or values, for short) and they belong to different datatypes (or types)

• 4à typeint• 4.0à typefloat• True,Falseà typebool• “hello”,“world”à typestr

>>>type(4)<class'int'>>>>type(4.0)<class'float'>>>>type(True)<class'bool'>>>>type("hello")<class'str'>>>>

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Atomic vs Composite

• We often differentiate between atomic values and composite values

• Anatomicvaluecannotbreakdownintosmallervalues(rememberatomsinPhysic?)

• Acompositevaluecanbebrokendownintosmaller/constituentvalues(inPhysic,amoleculecanbebrokendownintoothermoleculesoratoms?)

• E.g. numbers (4, 4.0) are atomic• Bool values (True/False) are also atomic

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Atomic vs Composite

• But strings (“hello”, “world”) are not atomic, since a string is a sequence of characters (i.e. a string consisting of only one character)

• “hello”à “h”,“e”,“l”,“l”,“o”• We can access (read) such characters by

for c in "hello":print(c)

Program

Outputofprogram

hello

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Other access methods

• Indexing (access one character)

• Slicing (access multiple characters)

for i in range(0, 5):print("hello"[i])

print("hello"[0:1])print("hello"[0:2])print("hello"[0:5])

Output

hhehello

Output

hello

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Why composite values?

• It is good to be able to group simple values into a composite value and process it as a bunch.

• Forexample:wecangroupfirstnameandsurnameintofullname• Firstname:“hung”• Surname:“nguyen duy”• Fullname:“hungnguyen duy”

• Using strings, we can group values that are strings themselves like the above example.

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Lists and List type

• But we can not group values that are not strings• Forexample:wecannotgroupfullname(string)withage(int)

• Fullname:“hungnguyen duy”• Age:18• “hungnguyen duy”18isnotalegalvalue

• List addresses this issue

• Basically, lists are composite values; and list type is a composite type

hungbib = ["hung nguyen duy", 18]print("hung's full name:", hungbib[0])print("hung's age:", hungbib[1])

Output

hungnguyen duy18

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Lists and List type

• A list can consist of values of any types, e.g. we can have

• Alistofnumbers• Alistofstrings• Alistofnumbersandstrings• Alistoflists

lofnum = [18,1998]lofstr = ["hung", "nguyen duy"]lofnumAndstr = ["hung", "nguyen duy", 18, 1998]lofl = [["hung", "nguyen duy"], [18, 1998]]

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The power of lists

• Using lists, we can write some programs we can not write by using only atomic values

• Example: Write a program to get (unknown) positive numbers from a user. If user inputs “-1”, then display all inputted numbers in an increasing order

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A failed attempt

# reserve some variables to store user’s numbersx1 = -1x2 = -1# xi = -1xn = -1

# read i = 0cont= Truewhile cont:

x = float(input("input a number"))if x==-1:

cont = Falseelse:

i = i +1xi = x

# sort

# display

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Solution

lonum = []# readcont= Truewhile cont:

x = float(input("input a number"))if x==-1:

cont = Falseelse:

lonum.append(x) # add x to the end# sortlonum.sort()# displayprint(lonum)

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List operations • Create

• lon =[1,3,2]• Access

• Indexing:lon[0],lon[1]• Slicing:lon[0:1],lon[0:2]

• Update• lon[0]=4

• Delete• dellon[1]• lon.remove(1)• lon.clear()

• Add to the end• lon.append(4)

• Concatenate• lon +[“hello”,“world”]

• Check memberships• xinlon

• Find length• len(lon)

• Sort• lon.sort()

• Find biggest, smallest• max(lon)• min(lon)

• etc

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Create

• Use [ , ]• Examples:

• Elements of a list can be pretty much anything (values, variables, and even functions)

lofnum = [18,1998]lofstr = ["hung", "nguyen duy"]lofnumAndstr = ["hung", "nguyen duy", 18, 1998]lofl = [["hung", "nguyen duy"], [18, 1998]]

lofnum = [18,1998]lofstr = ["hung", "nguyen duy"]lofl = [lofnum,lofstr]lofunc = [print, sum]lofunc[0](lofunc[1](lofnum))

Output

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Access

• Indexing: aList[anIndex]• Examples in the book (p 112)

A = ["Supperman", "Batman", "Spiderman",\"Snoopy", "Peterpan"]print(A[0])print(A[2])

Output

SupermanSpiderman

A = ["Supperman", "Batman", "Spiderman",\"Snoopy", "Peterpan"]print(A[-1])print(A[-2])

Output

PeterpanSnoopy

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How a list is indexed?

"Supperman" "Batman" "Spiderman" "Snoopy" "Peterpan"

0 1 2 3 4

-5 -4 -3 -2 -1

A[0] = A[0-len(A)]A[1] = A[1-len(A)]..................A[len(A)-1] = A[len(A)-1–len(A)]

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Access

• Slicing: aList[start:stop]

A = ["Supperman", "Batman", "Spiderman",\"Snoopy", "Peterpan"]print(A[1:4])print(A[0:1])

Output

['Batman','Spiderman','Snoopy']['Supperman']

A = ["Supperman", "Batman", "Spiderman",\"Snoopy", "Peterpan"]print(A[-3:-1])

Output

['Spiderman','Snoopy']

A = ["Supperman", "Batman", "Spiderman",\"Snoopy", "Peterpan"]print(A[:1]) # short for A[0:1]print(A[1:]) # short for A[1:5]print(A[:]) # short for A[0:5] 17

Access a list in a list

"Supperman" "Batman" "Snoopy" "Peterpan"

0 1 2 3 4

0 1

”Spider" ”man"

A = ["Supperman", "Batman", ["Spider", "man"],\"Snoopy", "Peterpan"]print(A[2][0])print(A[2][1])

Output

Spiderman

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Update

• Use assignment: aList[anIndex] = ....• Examples in the book (p 114)

E = [10,20,30]E[1] = 500print(E)

Output

[10,500,30]

E = [10,20,30]E[3] = 500print(E)

Errormessage

IndexError:listassignmentindexoutofrange

E = [10,20,30]E[1] = [1,2,3]print(E)

Output

[10,[1,2,3],30] 19

Delete elements

• del aList[anIndex] removes one element

• aList.remove(value) removes the first element whose value = value

• aList.clear() removes all elements

E = [10,20,30]del E[1]print(E)

Output

[10,30]

E = [10,20,30,20]E.remove(20)print(E)

Output

[10,30,20]

E = [10,20,30,20]E.clear()print(E)

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Add to the end

• aList.append(value)E = [10,20,30]E.append(500)print(E)

Output

[10,20,30,500]

E = [10,20,30]for i in range(5):

E.append(i)print(E)

Output

[10,20,30,0,1,2,3,4]

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Other operations

• Concatenation: aList1 + aList2

• Check membership

E = [10,20,30]x=0print([x+1]+ E)

Output

[1,10,20,30]

E = [10,20,30]x=0if x in E:

print("x is in E")else:

print("x is not in E")

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Other operations

• Iteration

• List comprehension (not in textbook, but I see in lab)

E = [10,20,30]for x in E:

print(x+1)

Output

112131

E = [10,20,30]N = []for x in E:

N.append(x+1)print(N)

Output

[11,21,31]

E = [10,20,30]N = [x+1 for x in E]print(N)

Output

[11,21,31]23

And more (see p 118)

• sum(aList)• sum([1,2,3])à 1+2+3

• len• len([1,2,3])à 3

• max• max([1,2,3])à 3

• min• min([1,2,3])à 1

• count• [1,2,3,1].count(1)à 2

• index• [1,2,3,1].index(1)à 0

• insert

• pop

• reverse, sort, ...

E = [10,20,30]E.insert(1,40)print(E) #[10, 40,20,30]

E = [10,20,30]x = E.pop() # x = 30, E = [10, 20]

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Kinds of list operations• As we have seen, sometimes we write aList.op(...), e.g.

• [1,2,3,1].count(1)• [1,2,3,1].index(1)• E.insert(1,40)

• But we also write op(aList), e.g.• sum([1,2,3])• len([1,2,3])• max([1,2,3])

• Operations of the first kind are called methods• Operations of the second kind are called functions• In this course we do not study the difference between

functions and methods. All you need to remember is the ways to use/call them.

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Lists in use

Problem: Write a program to get a string from user, and check if it is “Cat”, “Rat” or “Bat”A = ["Cat", "Rat", "Bat"]x = input("Which animal u want to see?")if x in A:

print("We have !")else:

print("We do not have")

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Lists in use

Problem: Write a function mysum(lon) to compute the sum of a given list of numbers# listOfnumber -> number# Ex: [1,2] -> 3 ; [1] -> 1; [] -> 0def mysum(lon):

s = 0for x in lon:

s = s + xreturn s

def mysum2(lon):s = 0for i in range(0, len(lon)):

s = s + lon[i]return s

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Problem solving (p 122)

Problem A: Write a program to get names from user (repeat until user input “x”) then display the names in alphabetical ordercont= Truelon = []while cont:

name= input("Give me a name")if name == "x":

cont = Falseelse:

lon.append(name)lon.sort()print(lon)

Output

GivemeanamehungGivemeanameaaGivemeanamebbGivemeanamex['aa','bb','hung']>>>

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Problem solving (p 122)

Problem B: Write a program to get many numbers from user (repeat until user inputs “-1”) then display only the numbers that are more than the average

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Problem solvingFull name Number grade Lettergrade

Nguyenduy Hung 20 D

Bunyarit Uyyanonvara 15 F

.... .... ....

Full name Number grade Lettergrade

Nguyenduy Hung 10 F

Bunyarit Uyyanonvara 35 C

Smart 100 A

... ... ...

ITS100

ITS101

When a semester ends, instructors submit grades to the registry. Write a program to help the registry to calculate GPA of each student in that semester. 30

its100 = [["nguyen duy hung", 20, "D"], ["Bunyarit Uyyanonvara", 15, "F"]]

its101 = [["Bunyarit Uyyanonvara", 35, "C"], ["nguyen duy hung", 10, "F"], ["Smart", 100, "A"]]

its102 = [["nguyen duy hung", 100, "A"], ["Smart", 90, "A"]]

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