Python | Accessing index and value in list

There are various methods to access the elements of a list, but sometimes we may require to access an element along with the index on which it is found. Let’s see all the different ways of accessing both index and value in a list.

Method #1: Naive method This is the most generic method that can be possibly employed to perform this task of accessing the index along with the value of the list elements. This is done using a loop. 

Python3

# Python3 code to demonstrate
# to get index and value
# using naive method

# initializing list
test_list = [1, 4, 5, 6, 7]

# Printing list
print("Original list is : " + str(test_list))

# using naive method to
# get index and value
print("List index-value are : ")
for i in range(len(test_list)):
    print(i, end=" ")
    print(test_list[i])

Output

Original list is : [1, 4, 5, 6, 7]
List index-value are : 
0 1
1 4
2 5
3 6
4 7

Time Complexity: O(n)
Auxiliary Space: O(1)

Method #2: Using list comprehension This method works in similar way as the above method but uses the list comprehension technique for the same, this reduces the possible lines of code to be written and hence saves time. 

Python3

# Python3 code to demonstrate
# to get index and value
# using list comprehension

# initializing list
test_list = [1, 4, 5, 6, 7]

# Printing list
print("Original list is : " + str(test_list))

# using list comprehension to
# get index and value
print("List index-value are : ")
print([list((i, test_list[i])) for i in range(len(test_list))])

Output

Original list is : [1, 4, 5, 6, 7]
List index-value are : 
[[0, 1], [1, 4], [2, 5], [3, 6], [4, 7]]

Time Complexity: O(n)
Auxiliary Space: O(1)

Method #3: Using enumerate() This is the most elegant method to perform this particular problem and is highly recommended to be used in case we require to get the index along with the value in the list. This method enumerates for index along with its value. 

Python3

# Python3 code to demonstrate
# to get index and value
# using enumerate

# initializing list
test_list = [1, 4, 5, 6, 7]

# Printing list
print("Original list is : " + str(test_list))

# using enumerate to
# get index and value
print("List index-value are : ")
for index, value in enumerate(test_list):
    print(index, value)

Output

Original list is : [1, 4, 5, 6, 7]
List index-value are : 
0 1
1 4
2 5
3 6
4 7

Time Complexity: O(n)
Auxiliary Space: O(1)

Method #4: Using zip() Another method that is basically used to bind the index with the corresponding value, zip() can also be possibly used to get index along with its value. 

Python3

# Python3 code to demonstrate
# to get index and value
# using zip()

# initializing list
test_list = [1, 4, 5, 6, 7]

# Printing list
print("Original list is : " + str(test_list))

# using zip() to
# get index and value
print("List index-value are : ")
for index, value in zip(range(len(test_list)), test_list):
    print(index, value)

Output

Original list is : [1, 4, 5, 6, 7]
List index-value are : 
0 1
1 4
2 5
3 6
4 7

Time Complexity: O(n)
Auxiliary Space: O(1)