Convert List of Lists to Flat List in Python (One Liner)

Suppose you have a list of lists like [[12, 45, 67], [34, 56], [88, 90, 78], [111]]. And you want to convert this to flat list like [12, 45, 67, 34, 56, 88, 90, 78, 111] then you can use Python one liner as follow:

list_of_lists = [[12, 45, 67], [34, 56], [88, 90, 78], [111]]

flat_list = [element for sub_list in list_of_lists for element in sub_list]

print("Flat list: ", flat_list)

Output

Flat list:  [12, 45, 67, 34, 56, 88, 90, 78, 111]

Above one liner code is equivalent to:

# one liner equivalent
flat_list = []
for sub_list in list_of_lists:
    for element in sub_list:
        flat_list.append(element)

Alternatively, you can use itertools as follows:

import itertools

list_of_lists = [[12, 45, 67], [34, 56], [88, 90, 78], [111]]

flat_list = list(itertools.chain(*list_of_lists))

print("Flat list: ", flat_list)