Accessing Elements

• We can access elements of the list either by using index or by using slice operator.

By using index

• List follows zero based index i.e. index of first element is zero.
• List supports both +ve and -ve indexes.
  • +ve index meant for Left to Right
  • -ve index meant for Right to Left

Example

my_list = [10,20,30,40]
print(my_list[0])
print(my_list[-1])
print(my_list[10])

Output

10
40
IndexError: list index out of range

By using slice operator

Syntax

subset_list = my_list[start, stop, step]

• start ⇒ It indicates the index where slice has to start. Default value is 0.
• stop ⇒ It indicates the index where slice has to end. Default value is length of the list.
• step ⇒ Increment value. Default value is 1.

Example

n=[1,2,3,4,5,6,7,8,9,10]
print(n[2:7:2])
print(n[4::2])
print(n[3:7])
print(n[8:2:-2])
print(n[4:100])

Output

[3, 5, 7]
[5, 7, 9]
[4, 5, 6, 7]
[9, 7, 5]
[5, 6, 7, 8, 9, 10]

Mutability

• Once we creates a List object, we can modify its content. Hence List objects are mutable.

Example

n=[10,20,30,40]
print(n)
n[1]=777
print(n)

Output

[10, 20, 30, 40]
[10, 777, 30, 40]

Traversing

• The sequential access of each element in the list is called traversal.

By using while loop

n=[0,1,2,3,4,5,6,7,8,9,10]
i=0
while i<len(n):
  print(n[i])
  i=i+1

Output

0
1
2
3
4
5
6
7
8
9
10

By using for loop

n=[0,1,2,3,4,5,6,7,8,9,]
for n1 in n:
  print(n1)

Output

0
1
2
3
4
5
6
7
8
9

Question

Display only even numbers from list of element.

n=[0,1,2,3,4,5,6,7,8,9,10]
for n1 in n:
  if n1%2==0:
    print(n1)

Output

0
2
4
6
8
10

Question

Display elements of list by index wise.

l=["A","B","C"]
x=len(l)
for i in range(x):
  print(l[i],"is available at positive index: ",i,"and at negative index: ",i-x)

Output

A is available at positive index:  0 and at negative index:  -3
B is available at positive index:  1 and at negative index:  -2
C is available at positive index:  2 and at negative index:  -1

Ungraded Questions

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