# In Python, nested lists are used for data storage and can be accessed using different methods.

A nested list is a list that contains other lists as its elements. This can make it easier to store complex or hierarchical structures of data. …

Updated November 28, 2023

A nested list is a list that contains other lists as its elements. This can make it easier to store complex or hierarchical structures of data.

What is a Nested List? A nested list in Python is a list that contains another list as an element or elements. It’s particularly useful for storing and manipulating complex structured data, like trees or nested arrays.

Here’s a simple example of how to create a nested list:

``````nested_list = [[1,2,3], [4,5,6], [7,8,9]]
print(nested_list) # Output: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
``````

The number of dimensions in a nested list is not restricted; it can be multi-dimensional to any depth. For example, `[[1, 2, [3, 4]], [5, 6, [7, 8, [9, 10]]]]` is also valid.

Accessing Nested Lists Python makes it easy to access nested lists by using indexing and slicing, along with list methods like `append()`, `insert()` etc., but the methods to access individual elements can differ depending on what the indexes represent - for example, they might be row or column numbers in a 2D array.

Here’s how to access an element in a nested list:

``````nested_list = [[1,2,3], [4,5,6], [7,8,9]]
print(nested_list[0][1]) # Output: 2
``````

We can also use negative indexing to count from the end of a nested list. For example, `nested_list[-1][-1]` would refer to the last element in the outermost list (which is the last element in the innermost list).

And if we want to iterate over each item in every sub-list, we can use nested loops:

``````for sublist in nested_list:
for item in sublist:
print(item)  # Outputs numbers from 1 to 9
``````

Remember that lists are mutable, meaning you can change them. If you need to modify a list in-place (without creating new ones), you can use methods like `pop()`, `remove()` etc. Here’s an example of removing the last element from each sublist:

``````for sublist in nested_list:
sublist.pop()  # This removes the last item in every sublist
print(nested_list)  # Outputs: [[1,2,3], [4,5,6], [7,8]]
``````

Summary In conclusion, Python’s list data structure is versatile and can be used to create complex hierarchical structures. By leveraging the features of lists, we can access elements in nested lists using indexing and slicing, modify them using methods like `append()`, `insert()` etc., and iterate over them easily with for-loops.