Flattening Lists in Python: 5 Essential Methods

The Power of List Comprehension

When it comes to flattening lists in Python, there’s no shortage of approaches. But some methods stand out for their elegance and efficiency. Take, for instance, the humble list comprehension. This Pythonic technique allows you to access each element of a sublist and store it in a new list, all in a single line of code.

my_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat_list = [num for sublist in my_list for num in sublist]
print(flat_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

The Traditional Approach: Nested for Loops

Of course, not everyone may be familiar with list comprehensions. No worries! A more traditional approach involves using nested for loops to iterate over each sublist and its elements.

my_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat_list = []
for sublist in my_list:
    for num in sublist:
        flat_list.append(num)
print(flat_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Leveraging the itertools Package

For those who prefer a more functional approach, the itertools package offers a convenient solution. The chain() method returns each element of each iterable (i.e., sublist), which can then be converted into a list using the list() function.

import itertools
my_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat_list = list(itertools.chain(*my_list))
print(flat_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

The sum() Method: A Surprisingly Effective Solution

Believe it or not, the humble sum() method can also be used to flatten lists. By providing two arguments – my_list and an empty list – sum() combines them to produce a flattened list.

my_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat_list = sum(my_list, [])
print(flat_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

The Lambda and reduce() Approach

Last but not least, we have the lambda and reduce() method combination. This approach applies a lambda function to all elements of my_list, effectively flattening the list.

import functools
my_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat_list = functools.reduce(lambda x, y: x + y, my_list)
print(flat_list)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

These five methods offer different approaches to flattening lists in Python. Whether you prefer the elegance of list comprehensions or the functionality of the itertools package, there’s a solution that’s right for you.