The difficulty is in that you need to write a regex, not a function.

The solution window for python doesn't have what function we are supposed to use. It just has this ‘PATTERN = re.compile(r’’)’ which isn’t a format I’ve ever seen on codewars before. Also, this seems way too easy to be a 4 kyu.

A few hints:

• sieve of Erosthenes is solid and fast way to generate primes; however, a lot depends on the implementation. I suggest to write your version and time it to generate primes up to 10^6, and try to improve it. You can use an online IDE, e.g. https://repl.it ; further hints: half sieve, "rwh primes"
• test small code snippets on http://www.pythontutor.com -- the less steps it requires, the faster it will be
• do more easy katas, e.g. about digits sum: there are much quicker ways to get the digit sum of a number
• don't repeat yourself (DRY): reuse your existing code -- don't write a validity chacker for each method, just call the existing one
• etc

Use conditional comments in the instructions so method's names are right for the current language. Also a starting code for javascript would be fine, just like there is one for other languages.

You have to add a method to String class.

Something doesn't seem to be right with the Javascript test. The instructions say is_uppercase but the test are isUpperCase but even changing the name of the function I still get not a function.

Man, the optimisation is what I'm enjoying most about this. Still not quite there though. It's a tricky one.

return something.

Fixed.

It was Python. Thx. Will do in the future.

Fixed.