How to iterate through a nested List in Python?

In this article, we are going to see how to iterate through a nested List. A list can be used to store multiple Data types such as Integers, Strings, Objects, and also another List within itself. This sub-list which is within the list is what is commonly known as the Nested List.

Iterating through a Nested List

Lets us see how a typical nested list looks like :

There are multiple ways to iterate through a Nested List:

Method 1: Use of the index to iterate through the list

Use of Positive Index:

Python3

# code
list = [10, 20, 30, 40, [80, 60, 70]]

# Printing sublist at index 4
print(list[4])

# Printing 1st element of the sublist
print(list[4][0])

# Printing 2nd element of the sublist
print(list[4][1])

# Printing 3rd element of the sublist
print(list[4][2])

Output:

[80, 60, 70]
80
60
70

Use of Negative Index

Python3

# code
list = [10, 20, 30, 40, [80, 60, 70]]

# Printing sublist at index 4
print(list[-1])

# Printing 1st element of the sublist
print(list[-1][-3])

# Printing 2nd element of the sublist
print(list[-1][-2])

# Printing 3rd element of the sublist
print(list[-1][-1])

Output:

[80, 60, 70]
80
60
70

Method 2: Use of loop to iterate through the list

Python3

# code
# LIST
list = [["Rohan", 60], ["Aviral", 21],
        ["Harsh", 30], ["Rahul", 40],
        ["Raj", 20]]

# looping through nested list using indexes
for names in list:
    print(names[0], "is", names[1],
          "years old.")

Output:

Rohan is 60 years old.
Aviral is 21 years old.
Harsh is 30 years old.
Rahul is 40 years old.
Raj is 20 years old.

Use of Temporary Variables inside a loop.

Python3

# code
# LIST
list = [["Rohan", 60], ["Aviral", 21],
        ["Harsh", 30], ["Rahul", 40],
        ["Raj", 20]]

# looping through nested list using multiple
# temporary variables
for name, age in list:
    print(name, "is",
          age, "years old.")

Output:

Rohan is 60 years old.
Aviral is 21 years old.
Harsh is 30 years old.
Rahul is 40 years old.
Raj is 20 years old.

Method 3: Use of Slicing

Python3

# code
# list
list = [10, 20, 30, 40,
        [80, 60, 70]]

# print the entire Sublist at index 4
print(list[4][:])

# printing first two element
print(list[4][0 : 2])

Output:

[80, 60, 70]
[80, 60]