# Python List Flattening : How to Convert a Nested List to Flat List – Best Techniques

- Link: https://techaid24.com/convert-nested-list-to-flat-list/
- Published: 2026-10-24T11:03:45+06:00
- Author: Anonymous Guest

In this article, we'll take a look at Show 1) Convert Nested List To Flat List In Python 1.1) Method 1: 1.2) Method 2: 1.3) Method 3: 2) Flatten List Using List Compression 3) Flatten List Using NumPy In this tutorial, we will go through several methods to convert a Nested list to flat list using Python. Lists are probably the most used data type in Python. Lists being mutable offer a lot of flexibility to perform a number of operations on the items of the list.   A list contains items separated by commas and enclosed within square brackets [ ].  Lists in Python can also have items of different data types together in a single list. A nested list is nothing but a list containing several lists for example [1,2,[3],[4,[5,6]]. Often we need to convert these nested lists to flat list to perform regular list operations on the data. Fortunately, in Python, there are many ways to achieve this.   Convert Nested List To Flat List In Python def flatten(li): return sum(([x] if not isinstance(x, list) else flatten(x) for x in li), []) print(flatten([1, 2, [3], [4, [5, 6]]])) 1234567  def flatten(li):     return sum(([x] if not isinstance(x, list) else flatten(x)            for x in li), [])  print(flatten([1, 2, [3], [4, [5, 6]]]))  Output: [1, 2, 3, 4, 5, 6] Method 1: import functools import operator li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = functools.reduce(operator.concat, li) print(flat_list) 12345678  import functools import operator  li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = functools.reduce(operator.concat, li) print(flat_list)  Output: [14, 215, 383, 87, 298, 374, 2, 3, 4, 5, 6, 7]   Method 2: from functools import reduce li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = reduce(lambda x, y: x+y, li) print(flat_list) 1234567  from functools import reduce  li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = reduce(lambda x, y: x+y, li) print(flat_list)  Output: [14, 215, 383, 87, 298, 374, 2, 3, 4, 5, 6, 7]   Method 3: This is one of the most efficient ways to flatten a large list. from itertools import chain li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = list(chain.from_iterable(li)) print(flat_list) 1234567  from itertools import chain  li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = list(chain.from_iterable(li)) print(flat_list)  Output: [14, 215, 383, 87, 298, 374, 2, 3, 4, 5, 6, 7]   Flatten List Using List Compression li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = [item for sublist in li for item in sublist] print(flat_list) 12345  li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = [item for sublist in li for item in sublist] print(flat_list)  Output: [14, 215, 383, 87, 298, 374, 2, 3, 4, 5, 6, 7]   Flatten List Using NumPy Note that, NumPy doesn’t come bundled with Python Installation you have to install it which can be done simply using Pip Installer. pip install numpy 123  pip install numpy  Once the installation is done you can run the code below, import numpy li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]] flat_list = list(numpy.concatenate(li).flat) print(flat_list) 1234567  import numpy li = [[14], [215, 383, 87], [298], [374], [2, 3, 4, 5, 6, 7]]  flat_list = list(numpy.concatenate(li).flat) print(flat_list)  Output: [14, 215, 383, 87, 298, 374, 2, 3, 4, 5, 6, 7]