How to flatten Nested Sequence in Python

Question

I have a nested sequence that I want to flatten into a single list of values.

What have you tried, and what exactly is the problem with it? Have you tried researching it, even? I know for a fact that there's more than one question on SO about this already. — jonrsharpe, Sep 08 '15 at 16:43
I'm going to say "no" to the "Have you tried researching it?" question, considering the first result for this title on Google (other than, now, this question) is [this duplicate](https://stackoverflow.com/questions/952914/making-a-flat-list-out-of-list-of-lists-in-python) which links to two more. — Two-Bit Alchemist, Sep 08 '15 at 18:28

score 2 · Answer 1 · edited Sep 08 '15 at 17:09

Please try this general solution: Write a recursive generator function involving a yield from statement. For example:

from collections import Iterable
def flatten(items, ignore_types=(str, bytes)):
    for x in items:
        if isinstance(x, Iterable) and not isinstance(x, ignore_types):
            yield from flatten(x, ignore_types)
        else:
            yield x
items = [1, 2, [3, 4, [5, 6], 7], 8]
# Produces 1 2 3 4 5 6 7 8
for x in flatten(items):
    print(x)

score 0 · Answer 2 · answered Sep 02 '16 at 20:31

I'd go with recursion but split in a balanced way.

def flatten(lst):
    n = len(lst)
    if n == 0:
        return lst
    elif n == 1:
        item = lst[0]
        try:
            return flatten(list(item))
        except TypeError:
            return [item]
    else:
        k = n // 2
        return flatten(lst[:k]) + flatten(lst[k:])

Demo

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

flatten(items)

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

How to flatten Nested Sequence in Python

2 Answers2

Demo