Flatten a List (iterator version) Flatten a List (iterator version)
English HU RU

Nicola likes to categorize all sorts of things. He categorized a series of numbers and as the result of his efforts, a simple sequence of numbers became a deeply-nested list. Sophia and Stephan don't really understand his organization and need to figure out what it all means. They need your help to understand Nikolas crazy list.

There is a list iterator which contains integers or other nested lists iterators which may contain yet more lists iterators and integers which then… you get the idea. You should put all of the integer values into one flat list. The order should be as it was in the original list with string representation from left to right.
After that you have to create an iterator object which is linked to this list.

We need to hide this program from Nikola by keeping it small. Because of this, your code should be shorter than 140 characters (with whitespaces) .

Input data: A nested list iterator with integers and other iterators.

Output data: An iterator object linked to the one-dimensional list with integers.


list(flat_list(iter([1, 2, 3]))) == [1, 2, 3]
list(flat_list(iter([1, iter([2, 2, 2]), 4]))) == [
                     1, 2, 2, 2, 4]
list(flat_list(iter([iter([2]), iter([4, iter([5, 6, iter([6]), 6, 6, 6]), 7])]))) == [
                     2, 4, 5, 6, 6, 6, 6, 6, 7]
list(flat_list(iter([-1, iter([1, iter([-2]), 1]), -1]))) == [
                     -1, 1, -2, 1, -1]

How it is used: This concept is useful for parsing and analyzing files with complex structures and task challenges that are checking your creativity in writing short code.

Precondition: 0 ≤ |array| ≤ 100
∀ x ∈ array : -2 32 < x < 2 32 or x is a list
depth < 10

Become Awesome

  • No Ads
  • No Limits
  • More Content
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

<< <
> >>
exec show

Whats Next?

Free accounts will see Best CheckiO solutions with some delay.
Best Solutions will be opened in
Become Awesome and Don't wait
The next stage is ""
Will be activated in
View More Solutions Random Review Solutions Go to the next mission