Please refer to List in Python Class 11 Computer Science notes and questions with solutions below. These revision notes and important examination questions have been prepared based on the latest Computer Science books for Class 11. You can go through the questions and solutions below which will help you to get better marks in your examinations.
Class 11 Computer Science List in Python Notes and Questions
7.1 Introduction:
- List is a collection of elements which is ordered and changeable (mutable).
- Allows duplicate values.
- A list contains items separated by commas and enclosed within square brackets ([ ]).
- All items belonging to a list can be of different data type.
- The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the list.
Difference between list and string:
7.2 Creating a list:
To create a list enclose the elements of the list within square brackets and separate the elements by commas.
Syntax: list-name= [item-1, item-2, …….., item-n]
Example:
mylist = [“apple”, “banana”, “cherry”] # a list with three items
L = [ ] # an empty list
7.2.1 Creating a list using list( ) Constructor:
o It is also possible to use the list( ) constructor to make a list.
mylist = list((“apple”, “banana”, “cherry”)) #note the double round-brackets print(mylist)
L=list( ) # creating empty list
7.2.2 Nested Lists:
>>> L=[23,’w’,78.2, [2,4,7],[8,16]]
>>> L
[23, ‘w’, 78.2, [2, 4, 7], [8, 16]]
7.2.3 Creating a list by taking input from the user:
>>> List=list(input(“enter the elements: “))
enter the elements: hello python
>>> List
[‘h’, ‘e’, ‘l’, ‘l’, ‘o’, ‘ ‘, ‘p’, ‘y’, ‘t’, ‘h’, ‘o’, ‘n’]
>>> L1=list(input(“enter the elements: “))
enter the elements: 678546
>>> L1 [‘6’, ‘7’, ‘8’, ‘5’, ‘4’, ‘6’]
# it treats elements as the characters though we entered digits
To overcome the above problem, we can use eval( ) method, which identifies the data type and evaluate them automatically.
>>> L1=eval(input(“enter the elements: “))
enter the elements: 654786
>>> L1
654786 # it is an integer, not a list
>>> L2=eval(input(“enter the elements: “))
enter the elements: [6,7,8,5,4,3] # for list, you must enter the [ ] bracket
>>> L2
[6, 7, 8, 5, 4, 3]
Note: With eval( ) method, If you enter elements without square bracket[ ], it will be considered as a tuple.
>>> L1=eval(input(“enter the elements: “))
enter the elements: 7,65,89,6,3,4 >>> L1
(7, 65, 89, 6, 3, 4) #tuple
7.3 Accessing lists:
- The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes.
- List-name[start:end] will give you elements between indices start to end-1.
- The first item in the list has the index zero (0).
Example: >>> number=[12,56,87,45,23,97,56,27]
number[2]
87 >>>
number[-1]
27
>>> number[-8]
12 >>> number[8]
IndexError: list index out of range
>>> number[5]=55 #Assigning a value at the specified index
number [12, 56, 87, 45, 23, 55, 56, 27]
7.4 Traversing a LIST:
Traversing means accessing and processing each element.
Method-1:
>>> day=list(input(“Enter elements :”))
Enter elements : sunday
>>> for d in day:
print(d)
Output:
s
u
n
d
a
y
Method-2
>>> day=list(input(“Enter elements :”))
Enter elements : wednesday
>>> for i in range(len(day)): print(day[i])
Output:
w
e
d
n
e
s
d
a
y
7.5 List Operators:
- Joining operator +
- Repetition operator *
- Slice operator [ : ]
- Comparison Operator <, <=, >, >=, ==, !=
- Joining Operator: It joins two or more lists.
Example: >>> L1=[‘a’,56,7.8] >>> L2=[‘b’,’&’,6] >>> L3=[67,’f’,’p’] >>> L1+L2+L3 [‘a’, 56, 7.8, ‘b’, ‘&’, 6, 67, ‘f’, ‘p’] - Repetition Operator: It replicates a list specified number of times.
Example: >>> L13 [‘a’, 56, 7.8, ‘a’, 56, 7.8, ‘a’, 56, 7.8] >>> 3L1 [‘a’, 56, 7.8, ‘a’, 56, 7.8, ‘a’, 56, 7.8] - Slice Operator:
List-name[start:end] will give you elements between indices start to end-1.
>>> number=[12,56,87,45,23,97,56,27]
>>> number[2:-2]
[87, 45, 23, 97]
>>> number[4:20]
[23, 97, 56, 27]
>>> number[-1:-6]
[ ]
>>> number[-6:-1]
[87, 45, 23, 97, 56]
number[0:len(number)]
[12, 56, 87, 45, 23, 97, 56, 27]
List-name[start:end:step] will give you elements between indices start to end-1 with skipping elements as per the value of step.
>>> number[1:6:2]
[56, 45, 97]
>>> number[: : -1]
[27, 56, 97, 23, 45, 87, 56, 12]
#reverses the list
List modification using slice operator:
>>> number=[12,56,87,45,23,97,56,27]
>>> number[2:4]=[“hello”,”python”]
>>> number
[12, 56, ‘hello’, ‘python’, 23, 97, 56, 27]
>>> number[2:4]=[“computer”] >>> number [12, 56, ‘computer’, 23, 97, 56, 27]
Note: The values being assigned must be a sequence (list, tuple or string)
Example: >>> number=[12,56,87,45,23,97,56,27]
>>> number=[12,56,87,45,23,97,56,27]
>>> number[2:3]=78 # 78 is a number, not a sequence
TypeError: can only assign an iterable
- Comparison Operators:
o Compares two lists
o Python internally compares individual elements of lists in lexicographical order.
o It compares the each corresponding element must compare equal and two sequences must be of the same type.
o For non-equal comparison as soon as it gets a result in terms of True/False, from corresponding elements’ comparison. If Corresponding elements are equal, it goes to the next element and so on, until it finds elements that differ.
Example:
L1, L2 = [7, 6, 9], [7, 6, 9]
L3 = [7, [6, 9] ]
For Equal Comparison:
For Non-equal comparison:
List Methods:
Consider a list:
company=[“IBM”,”HCL”,”Wipro”]
Deleting the elements from the list using del statement:
Syntax:
del list-name[index] # to remove element at specified index del list-name[start:end] # to remove elements in list slice
Example:
>>> L=[10,20,30,40,50]
>>> del L[2] # delete the element at the index 2
>>> L
[10, 20, 40, 50]
>>> L= [10,20,30,40,50]
>>> del L[1:3]
# deletes elements of list from index 1 to 2.
>>> L
[10, 40, 50]
>>> del L # deletes all elements and the list object too.
>>> L
NameError: name ‘L’ is not defined
Difference between del, remove( ), pop( ), clear( ):
Difference between append( ), extend( ) and insert( ) :
ACCESSING ELEMENTS OF NESTED LISTS:
Example:
L=[“Python”, “is”, “a”, [“modern”, “programming”], “language”, “that”, “we”, “use”]
L[0][0]
‘P’
L[3][0][2]
‘d’
https://pythonschoolkvs.wordpress.com/ Page 73
L[3:4][0]
[‘modern’, ‘programming’]
L[3:4][0][1]
‘programming’
L[3:4][0][1][3]
‘g’
L[0:9][0]
‘Python’
L[0:9][0][3]
‘h’
L[3:4][1]
IndexError: list index out of range
Programs related to lists in python:
Program-1 Write a program to find the minimum and maximum number in a list.
L=eval(input(“Enter the elements: “))
n=len(L)
min=L[0]
max=L[0]
for i in range(n):
if min>L[i]:
min=L[i]
if max<L[i]:
max=L[i]
print(“The minimum number in the list is : “, min)
print(“The maximum number in the list is : “, max)
Program-2 Find the second largest number in a list.
L=eval(input(“Enter the elements: “))
n=len(L)
max=second=L[0]
for i in range(n):
if maxsecond:
max=L[i]
seond=max
print(“The second largest number in the list is : “, second)
Program-3: Program to search an element in a list. (Linear Search).
L=eval(input(“Enter the elements: “))
n=len(L)
item=eval(input(“Enter the element that you want to search : “))
for i in range(n):
if L[i]==item:
print(“Element found at the position :”, i+1)
break
else:
print(“Element not Found”)
Output:
Enter the elements: 56,78,98,23,11,77,44,23,65
Enter the element that you want to search : 23
Element found at the position : 4
