‏‏chap6 list tuples.pptx

CS303E Slideset 2: 1
CS303E Slideset 2: 1 Simple Python
Python
Foundation of Computer Programming
CYBR 3511
Lecture 6
Lists and Tuples

Python
2
Topics
 Lists
 Functions and Methods for Lists
 Tuples
 Functions and Methods for Tuples

Python
3
Lists
A list an ordered sequence of items of any type.
lists are mutable. If we change a list, it doesn’t create
a new copy; it changes the actual contents of the list.

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4
Creating Lists
 Creating a simple list L: L= [1,2,3]
 Lists can be created with the l i s t class constructor
>>> l i s t ( )
[ ]
>>> l i s t ( [ 1 , 2, 3] )
# c r eat e em
pt y l i s t , w
i t h c ons t r uc t or
# c r eat e l i s t [ 1, 2, 3]
[ 1, 2, 3]
>>> l i s t ( [ " red " , 3, 2 . 5 ] ) # c r e a t e heterogeneous l i s t
# c r e a t e l i s t , no e x p l i c i t c o n s t r u c tor
# not an a c t u al l i s t
# c r e a t e l i s t using range
# c r e a t e c h a r a c te r l i s t from s t r i n g
[ ’ r ed’ , 3, 2. 5]
>>> [ " r ed" , 3, 2. 5]
[ ’ r ed’ , 3, 2. 5]
>>> r ange ( 4)
r ange ( 0, 4)
>>> l i s t ( r ange ( 4) )
[ 0, 1, 2, 3]
>>> l i s t ( " abc d" )
[ ’ a ’ , ’ b ’ , ’ c ’ , ’d ’ ]

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5
Slicing Lists
 Similar to strings as well, lists can be sliced
 To slice elements within a range start_index and end_index
(inclusive), we can use [start_index : end_index+1]
 >>> grades = ["A", "B", "C", "D", "F"]
 >>> grades[1:3]
 ['B', 'C']
 To slice elements from the beginning to a certain ending
index (inclusive), we can use [: end_index+1]
 >>> grades[:3]
 ['A', 'B', 'C']
A B C D F
0 1 2 3 4

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6
Sequence Operations
Lists are sequences and inherit various functions
from sequences.
Function
x in s
Description
x is in sequence s
x not in s
s1 + s2
s * n
s [ i ]
s [ i : j ]
len(s)
min(s)
max(s)
sum(s)
for loop
<, <=, >, >=
==, !=
x is not in sequences
concatenates two sequences
repeat sequence s n times
ith element of sequence (0-based)
slice of sequence sfrom i to j-1
number of elements in s
minimum element of s
maximum element of s
sum of elements in s
traverse elements of sequence
comparestwo sequences
compares two sequences

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7
Calling Functions on Lists
>>> l 1 = [ 1, 2, 3, 4, 5]
>>> l en( l 1 )
5
>>> m
i n( l 1 )
1
>>> m
ax( l 1 )
5
>>> s um
( l 1 )
# assumes elements are comparable
# assumes elements are comparable
# assumes summing makes sense
15
>>> l 2 = [ 1, 2, " r ed" ]
>>> s um
( l 2 )
Tr ac ebac k ( m
os t r ec ent c al l l as t ) :
Fi l e " <s t di n >" , l i ne 1, i n <m
odul e >
TypeE r r o r : unsupported operand type ( s ) f or + : ’ i n t ’ and ’ s t r
’
>>> m
i n( l 2 )
Tr ac ebac k ( m
os t r ec ent c al l l as t ) :
Fi l e " <s t di n >" , l i ne 1, i n <m
odul e >
TypeE r r o r : ’ < ’ not supported between i n s t a n c e s of ’ s t r ’ and
’ i nt ’
>>>

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8
Methods for Lists
These are methods from class list.
Since lists are mutable, these actually change t.
Function
t.append(x)
Description
add x to the end of t
t.count(x)
t.extend(l1)
t.index(x)
t . i n s e r t ( i , x)
t.pop()
t.pop(i)
t.remove(x)
t.reverse()
t . s o r t ( )
number of times x appearsin t
append elements of l1 to t
index of first occurence of x in t
insert x into t at position i
remove and return the last element of t
remove and return the ith element of t
remove the first occurenceof x from t
reverse the elements of t
order the elements of t

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9
Example
>>> l1 = [1 , 2 , 3]
>>> l1 . append (4) # add 4 to the end of l1
>>> l1 # note : changes l1
[1 , 2 , 3 , 4]
>>> l1 . count (4) # count occurrences of 4 in l1
1
>>> l2 = [5 , 6 , 7]
>>> l1 . extend ( l2 ) # add elements of l2 to l1
>>> l1
[1 , 2 , 3 , 4 , 5 , 6 , 7]
>>> l1 . index (5) # where does 5 occur in l1 ?
4
>>> l1 . insert (0 , 0) # add 0 at the start of l1
>>> l1 # note new value of l1
[0 , 1 , 2 , 3 , 4 , 5 , 6 , 7]
>>> l1 . insert (3 , ’a’) # lists are heterogenous
>>> l1
[0 , 1 , 2 , ’a’, 3 , 4 , 5 , 6 , 7]
>>> l1 . remove (’a’) # what goes in can come out
>>> l1
[0 , 1 , 2 , 3 , 4 , 5 , 6 , 7]

Python
10
Traversing List with a For Loop
Method2:
for i in range(len(mylist)):
body
f or u i n [ 2, 3, 5, 7] :
pr i nt ( u, end=" " )
Method1
for u in l i s t :
body
myList = [1, 2, 3]
for i in range(len(myList)):
print(myList[i], end = " ")
print()

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11
Get a list as input from user
# creating an empty list
lst = []
# number of elements as input
n = int(input("Enter number of elements : "))
# iterating till the range
for i in range(0, n):
n = int(input("Enter the element “,i,”:”))
lst.append(element )
# adding the element

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12
Multi-Dimensional Lists
 Lists can be nested so as to create a multi-dimensional
list
>>> myList = [[1, 2, 3], [4, 5, 6]]
>>> myList[0]
[1, 2, 3]
>>> myList[0][0]
1
>>> myList[0][1]
2
>>> myList[1][0]
4
>>>

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13
Traversing Multi-Dimensional Lists
 How can we iterate over the elements of a n-dimensional
list?
 By using n loops
my2DList = [[1, 2, 3], [4, 5, 6]]
for i in range(len(my2DList)):
for j in range(len(my2DList[i])):
print(my2DList[i][j], end = " ")
print()
1 2 3
4 5 6
Output:

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14
Tuples
A tuple is essentially an immutable list. Below is a list with three
elements and a tuple with three elements:
Tuples are enclosed in parentheses
Indexing and slicing work the same as with lists.
As with lists, you can get the length of the tuple by using the len
function, and, like lists, tuples have count and index methods.
However, since a tuple is immutable, it does not have any of the
other methods that lists have, like sort or reverse, as those
change the list.
L = [1,2,3]
t = (1,2,3)
t1 = (1, 2, 3)
t2 = (“a”, “b”, “c”, ”d”)
print(t1)
print(t2)

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15
Tuples
 Like lists, tuples can:
 Contain any and different types of elements
 Contain duplicate elements (e.g., (1, 1, 2))
 Be indexed exactly in the same way (i.e., using the [ ]
brackets)
 Be sliced exactly in the same way (i.e., using the [::]
notation)
 Be concatenated (e.g., t = (1, 2, 3) + (“a”, “b”, “c”))
 Be repeated (e.g., t = (“a”, “b”) * 10)
 Be nested (e.g., t = ((1, 2), (3, 4), ((“a”, “b”, ”c”), 3.4))
 Be iterated over

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Functions and Methods for Tuples
 Python provides two built-in methods that you can
use on tuples.
 count(x)
 Index(x)
t1 = (1, 2, 3, 1, 5, 1)
print(t1.count(1))
print(t1.index(1))
The count(x) function returns the number of
elements with the specified value x (e.g., x is 1
in this example)
The index(x) function returns the index of
the first element with the specified value x
(e.g., x is 1 in this example)
Output:
3
0
In fact, Python has only these two built-in functions that can be
used on tuples

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17
Example: Matrix-Matrix Addition
1 4 7 9 12
10 7 55 12 13
7 81 90 17 8
11 2 3 1 66
34 52 97 8 22
5×5 Matrix A
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
5×5 Matrix B
+ =
2 6 10 13 17
16 14 63 21 23
18 93 103 31 23
27 19 21 20 86
55 74 120 32 47
5×5 Matrix C

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18
import random
def buildSquareMatrix(m, n):
if m == n:
matrix = []
for i in range(m):
row = []
for j in range(n):
row.append(random.randint(1, 100))
matrix.append(row)
return matrix
else:
return "This function builds only square matrices with random
integersn"

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19
#This function assumes equal square matrices (i.e., each matrix is a square matrix
#and both have the same numbers of rows and columns)
def addMatrices(a, b):
m = n = len(a)
c = []
for i in range(m):
row = []
for j in range(n):
row.append(a[i][j] + b[i][j])
c.append(row)
return c

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def printMatrix(a):
for i in a:
for j in i:
print(j, end = "t")
print()
print()
a = buildSquareMatrix(5, 5)
b = buildSquareMatrix(5, 5)
printMatrix(a)
printMatrix(b)
c = addMatrices(a, b)
printMatrix(c)

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21
Exercises
 Q1:Write a function to sum all the items in a list list1.
Input
list1 = [5, 10, 15]
Output
Result : 30
 Q2:Write a function to get the largest number from a list list1
Input
list1 = [5, 10, 15]
Output
Result : 15
 Q3: Write a function to count the number of elements x in a list list1
Input
list1 = [5, 5, 20,5]
x=5
Output
Result : 3
 Q4:Write a function to multiply all the items in a list list1
Input
list1 = [5, 2, 20]
Output
Result : 200

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22
Exercises
 Q5: Write a function to find value x in a given list list1 , and if it is
present, replace it with 200. Only update the first occurrence of an item.
Input
list1 = [5, 10, 15, 20, 25, 50, 20]
x=20
Output
Result : [5, 10, 15, 200, 25, 50, 20]
 Q6: Write a function to square each element of a list.
Input
list1 = [2, 3, 4, 5, 6]
Output
Result : 4 9 16 25 36
 Q7: Write a function to filter odd and even number from a list.
Input
Given [2, 23, 24, 51, 46, 67]
Output
Even [2, 24, 46] Odd [23, 51, 67]

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23
Exercises
 Q8: Write a function to remove all occurrences of item x in a given list
list1 .
Input
list1 = [5, 10, 15, 20, 25, 50, 20]
X=20
Output
Result : [5, 10, 15, 25, 50]
 Q9: Write a function to remove duplicate items from a given list list1.
Input
list1= [2,3,4,5,2,6,3,2]
Output
Result: [2, 3, 4, 5, 6]

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24
HomeWork2
 Q1: Write a function to get the frequency of all elements in a list.
Input
list1 = [3, 5, 4, 3, 3, 4, 5, 2]
Output
The list frequency of elements is :
Element Frequency
3 3
5 2
4 2
2 1
 Q2: Write a 3 functions to find
• The union between two lists A and B
• The intersection between two lists A and B
• The difference between two lists A and B
Input
A = [1, 5, 4,2]
B= [1, 10, 2]
Output
Union(A,B): [1, 5, 4,2,10]
Intersection(A,B): [1,2]
Difference (A,B): [5,4]

‏‏chap6 list tuples.pptx

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