15-112 Fundamentals of Programming

Lecture 8September 14 , 2017

Announcements

Read pages 74 – 77

What are we doing today?

ListsList functions

Lists – Lets start with the “why”

Given a sequence of numbers, how do you find the minimum value?How do you find: max, sum, average?How do you find: How many numbers are

above average?

Lists as sequence of values

Variables can hold one value at a timeLists can hold a number of different values

Create a list

A simple listmyList = [1, 4, 5, 8, 12]

An initialized listmyList = [0] * 5myList[0,0,0,0,0]

Adding element to a lista = [0] * 5b= 12a = a + [b]a [0,0,0,0,0,12]

Creating Lists

Combining two listsmyList = [1, 4, 5, 8, 12]yourList = [3,7,4,9]ourList = myList + yourList ourList would be [1, 4, 5, 8, 12, 3, 7, 4, 9]

Accessing Elements

a = [2, 3, 5, 7, 11, 13]print a[0]print a[2]print a[-1]print a[-3]print a[0:2]print a[1:4]print a[1:6:2]

2

13

5

7[2,3]

[3, 7, 13]

[3, 5, 7]

Modifying Elements

a = [2, 3, 5, 7, 11, 13]

print aa[2] = 0print a

[2, 3, 5, 7, 11, 13]

[2, 3, 0, 7, 11, 13]

More List Operations

Slicing a ListmyList [1, 4, 5, 200, 12]print myList[1:3] [4, 5]

Assigning Value to a slicemyList[1:3] = [6,6,6,6]myList[1, 6, 6, 6, 6, 200, 12]

Finding Elements

Check for list membership: using “in”

a = [ 2, 3, 5, 2, 6, 2, 2, 7 ]print "a =", aprint (2 in a)print (4 in a)

Looping over Lists

a = [ 2, 3, 5, 7 ]

for item in a:print item

Exercise

Write a function called isSubset, that takes two lists as input parameters. The function should return True if all elements of first list are in second list.

Do you know the following about lists?

Can you declare an empty list?Can you declare a list with 5 1’s?Can you print the last element in a list?Can you access each element in a list using

a loop?Can you check if an element exists in a list?

So what’s the outputa = [2,3,6,7,1,4,8,8,8]for i in range(0,3):

print a[i*3+0],a[i*3+1],a[i*3+2]

a = [3,2,1,6,4,8,7,7,5]for i in range(0,3):

print a[i],a[i+3],a[i+6]

Output?def fun2(x,y):

for i in range(1,len(y)):if x[i] == y[-i]:

print i

fun2([7,3,5,2,4,8],[7,3,4,2,7,3])

Representing Data using lists

We can use lists to represent 1-D data. Grades of all students in Quiz1

How about 2-D data using a list? Grades of all students in all quizzes.

Tic-Tac-Toe

Suppose we have a list that represents a tic-tac-toe board. How big should be the list? How should we initialize it?

1 2 3

4 5 6

987

[1,2,3,4,5,6,7,8,9]

Printing the board

How do we print this list so it looks like a board?

printBoard(mylist)?

1 2 3

4 5 6

987

[1,2,3,4,5,6,7,8,9]

Accessing an element

How do I get an element at row 0, column 2

getElement(board,row,column)?

1 2 3

4 5 6

987

[1,2,3,4,5,6,7,8,9]

Setting an element

How do I set an element at row 0, column 2

setElement(board,row,column,player)?

1 2 3

4 5 6

987

[1,2,3,4,5,6,7,8,9]

Winning

How do we know if a player won?

gameWon(board,player)?

1 2 3

4 5 6

987

[1,2,3,4,5,6,7,8,9]

2-D lists

We have seen lists that hold integers, booleans, strings, etc.Can lists also hold other lists? [[1,2,3],[4,5,6],[7,8,9]]

+ How many elements in the above list? [1,2,[7,’a’,True],5,8]

+ How many elements in this list?

Accessing Elements in 2-D listsa = [[1,2,3],[4,5,6],[7,8,9]]

Reading valuesprint a[0][1]

Writing valuesa[1][0] = 12print a

[[1,2,3],[12,5,6],[7,8,9]]

Tic-Tac-Toe with 2-D lists

Suppose we use a 2D-list to represent a tic-tac-toe board. How big should be the list? How should we initialize it?

1 2 3

4 5 6

987

[[1,2,3],[4,5,6],[7,8,9]]

Printing the board

How do we print this list so it looks like a board?

printBoard(mylist)?

1 2 3

4 5 6

987

[[1,2,3],[4,5,6],[7,8,9]]

Accessing an element

How do I get an element at row 0, column 2

getElement(board,row,column)?

1 2 3

4 5 6

987

[[1,2,3],[4,5,6],[7,8,9]]

Setting an element

How do I get an element at row 0, column 2

setElement(board,row,column,player)?

1 2 3

4 5 6

987

[[1,2,3],[4,5,6],[7,8,9]]

Winning

How do we know if a player won?

gameWon(board,player)?

1 2 3

4 5 6

987

[[1,2,3],[4,5,6],[7,8,9]]

Strings

Strings are immutable Once created, a string itself cannot be

changed You can assign a different string to an existing

variablesname = “Daun Chung"name.lower()print namename = name.lower()print name

String Functions

s.count(sub) – Count the number of occurrences of sub in s

name = “Daun Chuung"print name.count(“u")print name.count(“uu")

String Functions

s.find(sub) Find the first index of sub in s, or -1 if not found

name = “Yasser El-Sayed"print name.find(“El")print name.find(“ “)print name.find(“Yasser")print name.find(“yasser")

String Functions

s.index(sub) – find the first index of sub in s or error if not found

name = “Yasser El-Sayed"print name.find(“El")print name.find(“ “)print name.find(“Yasser")print name.find(“yasser")

String Functions

s.rfind(sub) – Find the last index of sub in s or -1 if not founds.rindex(sub) – Find the last index of sub

in s or Error if not found

String Functions

s.split() – Returns a list of words in s

name = “Muhammad Ali Najeeb Qazi"eachName = name.split()print eachName

OUTPUT [‘Muhammad', ‘Ali', ‘Najeeb‘, ‘Qazi’]

String Functions

s.join(lst) – Join the list of words into a single string using s as separator

a = ["Harry", "Potter","and","the","goblet","of","fire"]t = " "print t.join(a) t = “..”print t.join(a)

Harry Potter and the goblet of fire

Harry..Potter..and..the..goblet..of..fire

Working with Strings

Count the number of vowels in a stringa = raw_input(“Enter something> ”)s = a.lower()print s.count(‘a’) + s.count(‘e’) +

s.count(‘i’) + s.count(‘o’) +s.count(‘u’)