Klarna Senior Python Backend Developer interview questions

Cod assignment: They asked me to create a web server with three math APIs(e.g. Fibonacci, ...) and to log the runtime of APIs, they gave me a review about my code, that the logger that I implemented is not efficient and so simple, but the point is that when I received the code assignment, I asked them about how do they need the logger to be implemented, is it OK to just write a simple custom logger or there are some other expectations that need to be satisfied, and they told me that I can write a custom one