Negative indexing
Python allows negative indexing for its sequences. The index of -1 refers to the last item, -2 to the second last item and so on.
n1=[‘c’ , ‘o’ , ‘m’ , ‘p’ , ‘u’ , ‘t’ , ‘e’ , ‘r’]
Positive indexing
|
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
|
c |
o |
m |
p |
u |
t |
e |
r |
|
-8 |
-7 |
-6 |
-5 |
-4 |
-3 |
-2 |
-1 |
Negative indexing
n1=[‘c’,’o’,’m’,’p’,’u’,’t’,’e’,’r’]
print(n1)
#output:
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’, ‘t’, ‘e’, ‘r’]
print(n1[-1])
#output:
r
print(n1[-2])
#output:
e
print(n1[-4])
#output:
u
Example:
n1=['c','o','m','p','u','t','e','r'] print(n1) print(n1[-1]) print(n1[-2]) print(n1[-4])
Output:
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’, ‘t’, ‘e’, ‘r’]
r
e
u
>>>
Example:
n2=[‘c’ , ‘a’ , ‘t’ , ‘a’ , ‘l’ , ‘y’ , ‘s’ , ‘t’]
Positive indexing
|
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
|
c |
a |
t |
a |
l |
y |
s |
t |
|
-8 |
-7 |
-6 |
-5 |
-4 |
-3 |
-2 |
-1 |
Negative indexing
n2=['c','a','t','a','l','y','s','t'] print(n2) print(n2[-0]) # -0 is 0 print(n2[-2]) print(n2[-5]) print(n2[-7]) print(n2[-1]) print(n2[1]) print(n2[4]) print(n2[6])
Output:
[‘c’, ‘a’, ‘t’, ‘a’, ‘l’, ‘y’, ‘s’, ‘t’]
c
s
a
a
t
a
l
s
>>>
How to slice lists in Python?
In list We can access a range of items by using the slicing operator “:” (colon).
print(n1[1:3])
#counting starts from 0
#will display elements from start to position -1
Example:
n1=[‘c’,’o’,’m’,’p’,’u’,’t’,’e’,’r’]
Positive Indexing
|
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
|
c |
o |
m |
P |
u |
t |
e |
R |
n1=[‘c’,’o’,’m’,’p’,’u’,’t’,’e’,’r’]
print(n1)
#output:
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’, ‘t’, ‘e’, ‘r’]
print(n1[1:3])
#output:
[‘o’, ‘m’]
print(n1[1:4])
#output:
[‘o’, ‘m’, ‘p’]
print(n1[1:5])
#output:
[‘o’, ‘m’, ‘p’, ‘u’]
print(n1[2:3])
#output:
[‘m’]
print(n1[2:4])
#output:
[‘m’, ‘p’]
print(n1[2:5])
#output:
[‘m’, ‘p’, ‘u’]
n1=['c','o','m','p','u','t','e','r'] print(n1) print(n1[1:3]) print(n1[1:4]) print(n1[1:5]) print(n1[2:3]) print(n1[2:4]) print(n1[2:5])
Output:
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’, ‘t’, ‘e’, ‘r’]
[‘o’, ‘m’]
[‘o’, ‘m’, ‘p’]
[‘o’, ‘m’, ‘p’, ‘u’]
[‘m’]
[‘m’, ‘p’]
[‘m’, ‘p’, ‘u’]
>>>
Example:
n1=[‘c’,’o’,’m’,’p’,’u’,’t’,’e’,’r’]
0 1 2 3 4 5 6 7
c o m p u t e r
|
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
|
c |
o |
m |
p |
u |
t |
e |
r |
print(n1)
#output
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’, ‘t’, ‘e’, ‘r’]
print(n1[:0])
#output
[]
print(n1[:1])
#output (Only position 0 with be displayed i.e. : 0 to 1-1)
[‘c’]
print(n1[:2])
Output: (only elements of position 0 to 2-1 will be displayed)
[‘c’, ‘o’]
print(n1[:3])
#output:
[‘c’, ‘o’, ‘m’]
print(n1[:4])
#output:
[‘c’, ‘o’, ‘m’, ‘p’]
print(n1[:5])
#output:
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’]
n1=['c','o','m','p','u','t','e','r'] print(n1) print(n1[:0]) print(n1[:1]) print(n1[:2]) print(n1[:3]) print(n1[:4]) print(n1[:5])
Output:
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’, ‘t’, ‘e’, ‘r’]
[]
[‘c’]
[‘c’, ‘o’]
[‘c’, ‘o’, ‘m’]
[‘c’, ‘o’, ‘m’, ‘p’]
[‘c’, ‘o’, ‘m’, ‘p’, ‘u’]
>>>
