The document discusses lists in Python. It defines mutable and immutable objects in Python and provides examples of lists as mutable objects. It describes how to create lists, access list elements using indexes and slicing, update and delete list elements, and various methods available for lists like append(), insert(), pop(), etc. It also discusses traversing lists, built-in functions for lists like len(), min(), max() etc. and arithmetic operations on lists.

1. LIST
Prepared by,
Prof. S. S. Gawali
Computer Engineering

2. WHAT IS MUTABLE IN
PYTHON?
▪ In Python programming language, whenever an object is susceptible to internal
change or the ability to change its values is known as a mutable object.
▪ Mutable objects in Python are generally changed after creation.
▪ The objects in Python which are mutable are provided below:
▪ Lists
▪ Sets
▪ Dictionaries
Computer Engineering PSP Prof. S. S.
Gawali 2

3. WHAT IS IMMUTABLE IN
PYTHON?
▪ When the objects in the Python are not susceptible to the internal change are known as
the immutable objects.
▪ They can not be modified once they are created.
▪ For example, int in Python is immutable hence they can not be modified once they are
created.
▪ Objects in Python which are immutable are shown below:
▪ int,
▪ float,
▪ bool,
▪ string,
▪ tuple
Computer Engineering PSP Prof. S. S.
Gawali 3

4. DIFFERENCES BETWEEN MUTABLE AND
IMMUTABLE
Mutable Immutable
The objects can be modified after the
creation as well.
Objects can not be modified after the
creation of the objects.
Example: Lists, Dicts, Sets, User-Defined
Classes, Dictionaries, etc.
Example: int, float, bool, string, Unicode,
tuple, Numbers, etc.
Computer Engineering PSP Prof. S. S.
Gawali 4

5. WHAT IS LIST?
▪ A list can be defined as a ordered collection of values or items of different types.
▪ Python lists are mutable type which implies that we may modify its element after it has
been formed.
▪ The items in the list are separated with the comma (,) and enclosed with the square
brackets [].
Computer Engineering PSP Prof. S. S.
Gawali 5

6. PROPERTIES OF LIST.
1) It is mutable
2) Ordered data type
3) Duplicates are allowed
4) Enclosed by []
5) List items are separated by comma
6) List is Dynamic
Computer Engineering PSP Prof. S. S.
Gawali 6

7. HOW TO CREATE LIST AND
DISPLAY LIST
▪ Syntax:
var = []
Example: Create list for Fruits
fruit=['Apple','Mango','Banana','Fig','Pineapple’]
Print(fruit)
l=[1,4,2,6,7]
print(l)
l1=[1, 'Apple',2.5,[1,2,3],(1,2,3),{'a',2}]
print(l1)
Output:
['Apple', 'Mango', 'Banana', 'Fig', 'Pineapple’]
[1,4,2,6,7]
[1, 'Apple', 2.5, [1, 2, 3], (1, 2, 3), {'a', 2}]
Computer Engineering PSP Prof. S. S.
Gawali 7

8. ACCESSING ELEMENTS OF
LIST
▪ In Python, there are two ways to access elements of List.
1. By using index
2. By using slice operator
Computer Engineering PSP Prof. S. S.
Gawali 8

9. ACCESSING CHARACTERS
BY USING INDEX:
▪ In Python, individual list element can be accessed by using the method of Indexing.
▪ Python support two types of index positive(+) and negative(-):
▪ Positive index: means left to right (forward direction)
▪ Negative index: means right to left (backward direction)
[10, 11, 12, 13, 14, 15, 16, 18, 19, 20]
0 1 2 3 4 5 6 7 8
9
+ve index
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 -ve index
Computer Engineering PSP Prof. S. S.
Gawali 9

10. EXAMPLE 1: USING POSITIVE
INDEXING
l=[10,11,12,13,14,15,16,18,19,20]
print(l[5])
print(l[2])
Output:
15
12
Computer Engineering PSP Prof. S. S.
Gawali 10

11. EXAMPLE 2: USING
NEGATIVE INDEXING
l=[10,11,12,13,14,15,16,18,19,20]
print(l[-5])
print(l[-2])
Output:
15
19
Computer Engineering PSP Prof. S. S.
Gawali 11

12. ACCESSING LIST ELEMENTS BY USING
SLICE OPERATOR:
Python also allows a form of indexing syntax that extracts multiple elements from a list,
known as list slicing.
If l is a list, an expression of the form l[m:n] returns the portion of l starting with
position m, and up to but not including position n.
Syntax:
String[beginindex:endindex:step]
Computer Engineering PSP Prof. S. S.
Gawali 12

13. EXAMPLE
Output:
[15, 16, 18, 19]
[12, 14, 16, 19]
[15, 16, 18]
[]
[19, 18, 16]
[10, 11, 12, 13, 14, 15, 16, 18, 19, 20]
[20, 19, 18, 16, 15, 14, 13, 12, 11, 10]
l=[10,11,12,13,14,15,16,18,19,20]
print(l[5:9])
print(l[2:9:2])
print(l[-5:-2])
print(l[-2:-5])
print(l[-2:-5:-1])
print(l[:])
print(l[::-1])
Computer Engineering PSP Prof. S. S.
Gawali 13

14. UPDATING LIST ELEMENTS USING INDEXING
AND SLICE OPERATOR
l=[1,2,4,5,6,7]
l[4]='Hi'
print(l)
l[2:6]=2,3,4,5
print(l)
Computer Engineering PSP Prof. S. S.
Gawali 14
Output
[1, 2, 4, 5, 'Hi', 7]
[1, 2, 2, 3, 4, 5]

15. ACCEPT LIST ELEMENTS
FROM USER
▪ Using for Loop:
▪ Syntax
Listvar=[input() for i in range(5)] # Accept 5 elements as String
Listvar=[int(input()) for i in range(5)] # Accept 5 elements as integer
▪ Example
l=[int(input()) for i in range(3)]
print(l)
l1=[input() for i in range(3)]
print(l1)
Output
1
2
3
[1, 2, 3]
5
4
3
['5', '4', '3']
Computer Engineering PSP Prof. S. S.
Gawali 15

16. ACCEPT LIST ELEMENTS
FROM USER
▪ Using Split() Method
▪ Syntax
Listvar=input().split()
▪ Example
l=input('Enter list elements by giving space between them ').split()
print(l)
l1=input('Enter list elements by giving - between them ').split('-’)
print(l1) Output:
Enter list elements by giving space between them 1 2 3
['1', '2', '3’]
Enter list elements by giving - between them 1-2-3
['1', '2', '3']
Computer Engineering PSP Prof. S. S.
Gawali 16

17. ACCEPTING LIST ELEMENTS
FROM USER
▪ Using eval()
▪ Syntax
Listvar=eval(input())
▪ Example
l1=eval(input("Enter list"))
print(l1)
Output
Enter list[1,2,2.4,'a','b',[3.5,'a’]]
[1, 2, 2.4, 'a', 'b', [3.5, 'a']]
Computer Engineering PSP Prof. S. S.
Gawali 17

18. len()
▪ This method used to returns number of elements in the list.
▪ Example
l=[1,2,'swap','my']
print(len(l))
Output
4
Computer Engineering PSP Prof. S. S.
Gawali 18

19. TRAVERSING LIST
ELEMENTS
▪ Using While Loop
▪ Forward Traversing:
l=[1,2,'swap','my']
i=0
while i<len(l):
print(l[i])
i+=1
Output
1
2
swap
my
Computer Engineering PSP Prof. S. S.
Gawali 19

20. TRAVERSING LIST
ELEMENTS
▪ Using Membership Operator
l=[1,2,'swap','my’]
for i in l:
print(i) Output
1
2
swap
my
Computer Engineering PSP Prof. S. S.
Gawali 20

21. TRAVERSING LIST
ELEMENTS
▪ Using While Loop
▪ Backward Traversing:
l=[1,2,'swap','my’]
i=-1
end=-len(l)-1
while i>end:
print(l[i])
i-=1
Output
my
swap
2
1
Computer Engineering PSP Prof. S. S.
Gawali 21

22. Deleting list elements using del keyword
del keyword used to delete object.
Example
l1=[4,6,2,8,9,10,9,5,8,7,9]
del l1[4]
print(f"List after del operation n {l1}")
del l1[2:5]
print(f"List after del operation n {l1}")
del l1[4:]
print(f"List after del operation n {l1}")
22
Output
List after del operation
[4, 6, 2, 8, 10, 9, 5, 8, 7, 9]
List after del operation
[4, 6, 9, 5, 8, 7, 9]
List after del operation
[4, 6, 9, 5]

23. min(), max() and sum()
▪ min() is used to return minimum of all the elements of List.
▪ Syntax:
min(list)
▪ max() is used to return maximum of all the elements of List.
▪ Syntax:
max(list)
▪ sum() is used to return sum of all elements of List.
▪ Syntax:
sum(list)
Computer Engineering PSP Prof. S. S.
Gawali 23

24. EXAMPLE
l=[1,2,3,6,102,456,899]
print("Minimum element in list is ",min(l))
print("Maximum element in list is ",max(l))
print("Sum of all elements in list is ",sum(l))
Output
Minimum element in list is 1
Maximum element in list is 899
Sum of all elements in list is 1469
Computer Engineering PSP Prof. S. S.
Gawali 24

25. sorted()
▪ sorted() returns new sorted list.
▪ The original list is not sorted.
▪ Syntax:
sorted(list)
▪ Example
l=[102,1,11,456,36,788,99]
print(sorted(l))
print(l)
Output:
[1, 11, 36, 99, 102, 456, 788]
[102, 1, 11, 456, 36, 788, 99]
Computer Engineering PSP Prof. S. S.
Gawali 25

26. ARITHMETICAL OPERATOR
FOR LIST
▪ + is used for concatenation/ join two list
▪ * is used for repetition of list
▪ += is used to append list with new list
▪ Example
l=[102,1,11,456,36,788,99]
l1=['swap','hi']
print(l+l1)
print(l*2)
l+=l1
print(l)
Output
[102, 1, 11, 456, 36, 788, 99, 'swap', 'hi']
[102, 1, 11, 456, 36, 788, 99, 102, 1, 11, 456, 36, 788,
99]
[102, 1, 11, 456, 36, 788, 99, 'swap', 'hi']
Computer Engineering PSP Prof. S. S.
Gawali 26

27. METHODS OF LIST
▪ append()
▪ insert()
▪ count()
▪ index()
▪ pop()
▪ remove()
▪ reverse()
▪ sort()
▪ extend()
Computer Engineering PSP Prof. S. S.
Gawali 27

28. append()
▪ Used for appending and adding elements to List.
▪ It is used to add elements to the last position of the List.
▪ Syntax
list.append (element)
▪ Example
l1=['bye','hi']
l1.append('welcome')
print(f"List after append operation n {l1}")
l1.append(['Hello','Hi'])
print(f"List after append operation n {l1}")
Output
List after append operation
['bye', 'hi', 'welcome']
List after append operation
['bye', 'hi', 'welcome', ['Hello','Hi']]
Computer Engineering PSP Prof. S. S.
Gawali 28

29. insert()
▪ Used to inserts an element at the specified position.
▪ Syntax:
▪ list.insert(position, element)
▪ Example
l1=['bye','hi','welcome','hello','bye']
l1.insert(2,'Namaste')
print(f"List after insert operation n {l1}")
Output
List after insert operation
['bye', 'hi', 'Namaste', 'welcome', 'hello', 'bye']
Computer Engineering PSP Prof. S. S.
Gawali 29

30. count()
▪ Used to calculates total occurrence of a given element of List.
▪ Syntax:
▪ List.count(element)
▪ Example
l1=['bye','hi','welcome','hello','bye']
c=l1.count('bye')
print(f"Bye occurs {c} times") Output
Bye occurs 2 times
Computer Engineering PSP Prof. S. S.
Gawali 30

31. index()
▪ Returns the index of the first occurrence. The start and End index are not necessary
parameters.
▪ Syntax:
▪ List.index(element[,start[,end]])
▪ Example
l1=['bye','hi','welcome','hello','bye']
i=l1.index('bye')
print(f"bye present at {i} index")
Output
bye present at 0 index
Computer Engineering PSP Prof. S. S.
Gawali 31

32. pop()
▪ Used to removes the element at the specified index from the list.
▪ Index is an optional parameter.
▪ If no index parameter, then removes last elements.
▪ Syntax:
▪ list.pop(index)
▪ Example
l1=['bye','hi','welcome','hello','bye']
l1.pop(2)
print(f"List after pop operation n {l1}")
l1.pop()
print(f"List after pop operation n {l1}")
Output
List after pop operation
['bye', 'hi', 'hello', 'bye']
List after pop operation
['bye', 'hi', 'hello']
Computer Engineering PSP Prof. S. S.
Gawali 32

33. remove()
▪ Used to remove or delete obj from the list.
▪ ValueError is generated if obj not present in the list.
▪ If multiple copies of obj exists in the list, then the first value is deleted.
▪ Syntax
List.remove(obj)
▪ Example
l1=['bye','hi','welcome','hello','bye']
l1.remove('bye')
print(f"List after remove operation n {l1}")
l1.remove('RamRam')
print(f"List after remove operation n {l1}")
List after remove operation
['hi', 'welcome', 'hello', 'bye']
ValueError: list.remove(x): x not in list
Computer Engineering PSP Prof. S. S.
Gawali 33

34. reverse()
▪ Used to reverses elements in the List .
▪ It just modifies the original list.
▪ Syntax
List.reverse()
▪ Example
l1=['bye','hi','welcome','hello','namaste']
print(f"List before reverse operation n {l1}")
l1.reverse()
print(f"List after reverse operation n {l1}")
Output
List before reverse operation
['bye', 'hi', 'welcome', 'hello', 'namaste']
List after reverse operation
['namaste', 'hello', 'welcome', 'hi', 'bye']
Computer Engineering PSP Prof. S. S.
Gawali 34

35. sort()
▪ Python list sort() function can be used to sort a List in ascending, descending, or
user-defined order.
▪ Syntax
List.sort(reverse=true/false, key=myfun)
reverse: (Optional), reverse=True will sort the list descending.
Default is reverse=False
key Optional. A function to specify the sorting criteria(s)
Computer Engineering PSP Prof. S. S.
Gawali 35

36. EXAMPLE: SORT IN
ASCENDING ORDER
▪ l1=[1,5,2,8,3,9,10,134,54,768]
▪ print(f"List before sort operation n {l1}")
▪ l1.sort()
▪ print(f"List after sort operation n {l1}")
Output
List before sort operation
[1, 5, 2, 8, 3, 9, 10, 134, 54, 768]
List after sort operation
[1, 2, 3, 5, 8, 9, 10, 54, 134, 768]
Computer Engineering PSP Prof. S. S.
Gawali 36

37. EXAMPLE: SORT IN
DESCENDING ORDER
▪ l1=[1,5,2,8,3,9,10,134,54,768]
▪ print(f"List before sort operation n {l1}")
▪ l1.sort(reverse=True)
▪ print(f"List after sort operation n {l1}")
Output
List before sort operation
[1, 5, 2, 8, 3, 9, 10, 134, 54, 768]
List after sort operation
[768, 134, 54, 10, 9, 8, 5, 3, 2, 1]
Computer Engineering PSP Prof. S. S.
Gawali 37

38. EXAMPLE: SORT IN ALPHABETICAL
ASCENDING ORDER
l1=['bye','hi','welcome','hello','namaste']
print(f"List before sort operation n {l1}")
l1.sort()
print(f"List after sort operation n {l1}")
Output
List before sort operation
['bye', 'hi', 'welcome', 'hello', 'namaste']
List after sort operation
['bye', 'hello', 'hi', 'namaste', 'welcome']
Computer Engineering PSP Prof. S. S.
Gawali 38

39. EXAMPLE: SORT IN ALPHABETICAL
DESCENDING ORDER
l1=['bye','hi','welcome','hello','namaste']
print(f"List before sort operation n {l1}")
l1.sort(reverse=True)
print(f"List after sort operation n {l1}")
Output
List before sort operation
['bye', 'hi', 'welcome', 'hello', 'namaste']
List after sort operation
['welcome', 'namaste', 'hi', 'hello', 'bye']
Computer Engineering PSP Prof. S. S.
Gawali 39

40. EXAMPLE: USER-DEFINE
ORDER SORTING
def sortSecond(val):
return val[1]
list1 = [[1,2],[2,4],[3,3]]
list1.sort(key=sortSecond)
print(list1)
list1.sort(key=sortSecond, reverse=True)
print(list1)
Computer Engineering PSP Prof. S. S.
Gawali 40
Output
[[1, 2], [3, 3], [2, 4]]
[[2, 4], [3, 3], [1, 2]]

41. extend()
▪ extend() method used to adds each element of the list, string, tuple,set to the end of
the List, modifying the original list.
▪ Syntax: list.extend(iterable)
▪ Parameters:
▪ iterable: Any iterable (list, set, tuple, etc.)
Computer Engineering PSP Prof. S. S.
Gawali 41

42. EXAMPLE
l=[1,2,3]
l1=['hi','bye’]
l2=(2,4)
l.extend(l1)
print(l)
l.extend(l2)
print(l)
Computer Engineering PSP Prof. S. S.
Gawali 42
Output
[1, 2, 3, 'hi', 'bye']
[1, 2, 3, 'hi', 'bye', 2, 4]

43. THANK YOU
Computer Engineering PSP Prof. S. S.
Gawali 43