Appending to 2D List in Python

A 2D list in Python is a list of lists where each sublist can hold elements. Appending to a 2D list involves adding either a new sublist or elements to an existing sublist. The simplest way to append a new sublist to a 2D list is by using the append() method.

a = [[1, 2], [3, 4]]

# Append a new sublist
a.append([5, 6])

print(a)

[[1, 2], [3, 4], [5, 6]]

Explanation:

• append() adds a new sublist [5, 6] as a single element to the 2D list.
• The original structure of the 2D list remains unchanged.

Let's explore some other methods to append to 2D List in Python

Appending to an Existing Sublist

If we want to append an element to an existing sublist in the 2D list, you can directly append it to that sublist.

a = [[1, 2], [3, 4]]

# Append an element to the second sublist
a[1].append(5)

print(a)

[[1, 2], [3, 4, 5]]

Explanation:

• Access the desired sublist using indexing (a[1]) then apply append() to add an element.
• This modifies the contents of the sublist while keeping the 2D structure intact.

Using +=

+= operator allows you to extend a sublist with multiple elements in a concise manner.

a = [[1, 2], [3, 4]]

# Extend the first sublist with multiple elements
a[0] += [5, 6]

print(a)

[[1, 2, 5, 6], [3, 4]]

Explanation:

• += modifies the sublist in place by appending elements from another list.
• This is equivalent to using extend().

Using List Comprehension

If we want to append multiple sublists dynamically list comprehension is a concise option.

a = [[1, 2], [3, 4]]

# Add multiple sublists
a += [[5, 6], [7, 8]]

print(a)

[[1, 2], [3, 4], [5, 6], [7, 8]]

Explanation:

• List comprehension generates sublists dynamically and appends them to the original list.
• This method is concise and maintains readability for batch operations.

Using extend() to Flatten a 2D List

If we wish to merge another 2D list into the current one extend() is an efficient choice.

a = [[1, 2], [3, 4]]

# Extend the 2D list with another 2D list
a.extend([[5, 6], [7, 8]])

print(a)

[[1, 2], [3, 4], [5, 6], [7, 8]]

Explanation:

• extend() adds elements of another iterable to the list without nesting.
• This method works well for combining two 2D lists.