Ordered by speed:

1. Fork #4
2. Fork #3
3. Fork #1
4. Fork #2
   So, yes, this one is the quickest.

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Because the numbers are bigger than integer max value?

How is it not working? It works exactly as specified in its documentation.

With this, I don't see that error, it's not a right solution, but you can see there is no error of the kind you mentioned.

def splitlist(lst):
    return [4, 27],[73]

Is your return line like this one?

return a, b # a and b are lists

Is the error the same as before?

Closing, because it is a problem with what your function returns.

If you don't return two lists, you'll get that error. a and b should be lists there.

Your task is to write a function splitlist(x), that will return two lists a and b, such that abs(sum(a)-sum(b)) is minimised.

Are you returning two lists?

that's on purpose. You need a better algorithm approach (without that requirement, this wouldn't be a blue kata)

I suggest you to complete a few hundred more katas to improve your understanding of the test framework and everything else around here, and then start making katas. Note your ideas in the meantime to be able to use them once you're ready.

Not a kata issue, it's a problem with your code, use Question label next time and it's better if you actually post your whole code, using markdown formatting, and mark your post as having spoiler content.