I did the same. I guess it's a remnants of numerous attempts to return string. A bit later, when I realise that solution requires list, I've changed return string to list, however convertion of two parts remained.

The parameter lines is already a string so no need to convert its expressions. Just the counter.

Note: above comment is true only for python 3 & not for python 2.

Use spoiler flag next time.

x can be greater than n? and other numbers will be negative to sum up to n? can you explain why x<n/2?

fuckin hell - brilliant

so you are checking for each unit increase in a string value? what if the minimum length of each string is 100... you are having to check from 1 to 100? did i catch your logic correctlly?