What Is a Nested Data Structure in Python?


Angela Bailey

What Is a Nested Data Structure in Python?

In Python, a nested data structure refers to the concept of storing one data structure inside another data structure. This allows you to create complex and hierarchical structures that can represent real-world scenarios more accurately.

Why Use Nested Data Structures?

Nested data structures are incredibly useful when you need to represent relationships or hierarchies between different pieces of data. They provide a way to organize and store related information together, making it easier to access and manipulate.

Let’s explore some common examples of nested data structures:

1. Lists within Lists

A list is a versatile and widely used data structure in Python. It can contain elements of any type, including other lists. By nesting lists within lists, you can create multi-dimensional structures.

Here’s an example:

my_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

This creates a list with three nested lists inside it. Each nested list represents a row of elements.

2. Dictionaries within Lists

Dictionaries are another powerful data structure in Python that allows you to store key-value pairs. You can also nest dictionaries within lists to create more complex structures.

Consider the following example:

my_data = [{'name': 'John', 'age': 25}, {'name': 'Jane', 'age': 30}]

This creates a list containing two dictionaries representing individuals’ information (name and age).

3. Lists within Dictionaries

The opposite is also possible – nesting lists within dictionaries. This can be useful when you want to associate multiple values with a single key.

my_dict = {'fruits': ['apple', 'banana', 'orange'], 'vegetables': ['carrot', 'spinach']}

This dictionary contains two keys, ‘fruits’ and ‘vegetables,’ each associated with a list of items.

Working with Nested Data Structures

Once you have created a nested data structure, accessing and manipulating its elements is straightforward using indexing and key-value pairs.

To access specific elements in a nested list, you can use multiple indices. For example:

print(my_list[0][1])  # Output: 2

This retrieves the element at index 1 of the first nested list in my_list.

For nested dictionaries, you can access values using multiple keys:

print(my_data[1]['name'])  # Output: Jane

This retrieves the value associated with the key ‘name’ in the second dictionary of my_data.

Nested Loops for Iteration

When working with deeply nested data structures, you may need to use nested loops for iteration.

for row in my_list:
    for element in row:

This code snippet iterates through each element in my_list and prints them individually. It effectively traverses all elements within the nested structure.


Nested data structures provide a powerful way to organize and represent complex relationships between data elements. By nesting different data structures like lists and dictionaries, you can create more meaningful structures that accurately reflect real-world scenarios. Understanding and working with nested data structures is a crucial skill for any Python developer.

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