5 Ways To Flatten A List In Python

There are many ways to flatten a list in Python, but in this article, I’m going to mention my top five favorites.

Let’s get started.

Way 1: Loop over individual lists and use append to construct a single list

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

full_list = []

for ls in lst:

  for item in ls:

     full_list.append(item)

print(full_list)

#output: [1,2,3,4,5]

In this approach, we are using nested loop (a.k.a. loop inside another loop) which is not considered as a good practice. So, let’s move on to next approach.

Way 2: Using extend function

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

full_list = []

for ls in lst:

   full_list.extend(ls)

print(full_list)

#output: [1,2,3,4,5]

Similar to extend(…) function, you can also use += and it will give you same result.

full_list += ls

Way 3: Using List comprehension

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

full_list = [item for ls in lst for item in ls]

print(full_list)

#output: [1,2,3,4,5]

Way 4: Using itertools

import itertools

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

full_list = list(itertools.chain.from_iterable(lst))

print(full_list)

Way 5: Using functools

import operator

import functools

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

full_list = functools.reduce(operator.iconcat,lst,[])

print(full_list)

#output: [1,2,3,4,5]

I hope you enjoyed learning all these 5 ways. In case of any doubts, please feel free to check out my video recording: