just the zen of python ;)
but the point I was focusing is the build-in filter

Enveloping a function into a class for no particular reason sure makes a lot of sense ;)

none of you read the title!
where is that filter???
checkout my solution!

this solution does also use a foor-loop

That's not what the description says. The input consists of non-negative ints and strings and you should throw out all the strings. No need to check for negative ints.

it should be non-negative....

I don't think either is more right. Yonog1's answer exactly matches the requirement "returns a new list with the strings filtered out" whereas yours techinically returns a new list of only integers. Assuming the input is limited to integers and strings as stated, either works.

Please mark your post as having spoiler content next time.

nice and clear what your list interpration is doing.